type M struct was never used (as far as I know).
type VariableEval interface was used for a brief period of time during
the refactoring, now both its methods are functions.

The authorization prompt on macOS can take a long time to be
acknowledged by the user, we should keep waiting for a connection as
long as the debugserver instance we launched remains alive.

Before this commit our temp breakpoints only checked that we would stay
on the same goroutine.
However this isn't enough for recursive functions we must check that we
stay on the same goroutine AND on the same stack frame (or, in the case
of the StepOut breakpoint, the previous stack frame).

This commit:
1. adds a new synthetic variable runtime.frameoff that returns the
   offset of the current frame from the base of the call stack.
   This is similar to runtime.curg
2. Changes the condition used for breakpoints on the lines of the
   current function to check that runtime.frameoff hasn't changed.
3. Changes the condition used for breakpoints on the return address to
   check that runtime.frameoff corresponds to the previous frame in the
   stack.
4. All other temporary breakpoints (the step-into breakpoints and defer
   breakpoints) remain unchanged.

Fixes #828

Debugserver does not work as documented, "--" needs to be specified to
pass arguments to the target process (but only if it's an argument that
starts with a dash).

Fixes #839

Fixes #836

You usually want to know the reason for the panic when a panic happens,
it can be printed manually this is a small quality of life improvement.

If CurrentThread isn't running a goroutine SelectedGoroutine can be
nil, do not blindly dereference it.

Fixes #827

Implements #727

While implementing the gdbserial backend everything was changed to call
Detach to "close" a process so that gdbserial could do its clean up in
a single place. However the native implementation of Detach does not
actually kill processes we launched.

Fixes #821

debugserver requires a special option to forward the environment to the target.

Fixes #818

Lldb-server does not currently support windows/amd64 (it's in
development). And delve's native backend seems to work well on windows.
Disable the lldb backend on windows for now.

Fixes #817

Fixes #809

* proc/native: remove unused utility methods

* proc: turn FindFileLocation, FindFunctionLocation, FirstPCAfterPrologue methods into function

* proc/eval: fix length calculation for string concatenation

* proc/variable: find package variables when the package has a path

Fixes #799

Go recently introduced proposal tags to their version tags, we
are simply allowing delve to handle it appropriately.

See:
https://github.com/golang/go/commit/0954fdd51e390e209317d4652d7effc15512fd50

- moved target.Interface into proc as proc.Process
- rename proc.IThread to proc.Thread
- replaced interfaces DisassembleInfo, Continuable and
  EvalScopeConvertible with Process.
- removed superfluous Gdbserver prefix from types in the gdbserial
  backend.
- removed superfluous Core prefix from types in the core backend.

- move native backend to pkg/proc/native
- move gdbserver backend to pkg/proc/gdbserial
- move core dumps backend to pkg/proc/core

- always print a header with the path to the file being displayed
- always evaluate the linespec argument, even if a scope prefix is present

Fixes #711, #713

Expressions such as:

 frame 0    list
 frame   0   list
 on abreakpoint     print x
 goroutine    1    frame     0     list

should all execute correctly

Fixes #712

Core files contain a variety of memory mappings either to files or
anonymous regions stored in the core file. These regions can overlap, so
figuring out what exactly to read can be tricky. This commit contains
a data structure, SplicedMemory, which accumulates mappings and reads
from the correct sources.

* pkg/proc: use golang.org/x/arch/x86/x86asm

instead of rsc.io/x86/x86asm

* pkg/dwarf: migrate to github.com/pkg/profile

from github.com/davecheney/profile

* scripts: keep script go files from being considered for the build

scripts/gen-*.go files are scripts for generating documentation
files and don't follow the typical Go package layout. Expected
usage is like

   go run scripts/gen-cli-docs.go

* vendor: update vendored packages

There were many changes in delve, and go tool chains since last
vendored package update. I just rerun godpes from scratch.

$ rm vendor/*
$ rm Godeps/Godeps.json
$ go list ./... | grep -v /vendor/ | grep -v /scripts/ | go get -u -t
$ go get -u github.com/mattn/go-colorable
$ go get -u github.com/mattn/go-isatty
$ go list ./... | grep -v /vendor/ | grep -v /scripts/ | godeps save

* proc: Refactor stackIterator to use memoryReadWriter and BinaryInfo

* proc: refactor EvalScope to use memoryReadWriter and BinaryInfo

* proc: refactor Disassemble to use memoryReadWriter and BinaryInfo

* proc: refactor BinaryInfo part of proc.Process to own type

The data structures and associated code used by proc.Process
to implement target.BinaryInfo will also be useful to support a
backend for examining core dumps, split this part of proc.Process
to a different type.

* proc: compile support for all executable formats unconditionally

So far we only compiled in support for loading the executable format
supported by the host operating system.
Once support for core files is introduced it is however useful to
support loading in all executable formats, there is no reason why it
shouldn't be possible to examine a linux coredump on windows, or
viceversa.

* proc: bugfix: do not resume threads on detach if killing

* Replace BinaryInfo interface with BinInfo() method returning proc.BinaryInfo

Detach did not work for processes we attach to via PID.

Linux: we were only detaching from the main thread, all threads are
detached independently

Windows: we must resume all threads before detaching.

macOS: still broken.

Updates #772

When running interactive command in gdb, it will remove beginning space,
so do the same for dlv, which will be more convient for user

We only use Registers.Get besides for evaluating the argument of a CALL
instruction so this doesn't matter in practice, but it's still wrong.

Stack barriers were removed in Go 1.9, and thus code that
expected various stack-barrier-related symbols to exist
does not find them.  Check for their absence and do not
crash when they are missing.  Disable stack-barrier-handling
test for 1.9 and beyond.

Fixes #754.

One of those goroutines could also conceivably be stopped on line 8.

The rest of the code uses Detach to "close" a proc.Process, the tests
should do the same.
Any cleanup that proc.Process needs to do can then be put inside Detach
and the tests will run it.