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

% go test -race -v -short

=== RUN   TestBuild
==================
WARNING: DATA RACE
Write at 0x00c4201379a0 by goroutine 9:
  os.(*file).close()
      /usr/local/go/src/os/file_unix.go:143 +0x10a
  os.(*File).Close()
      /usr/local/go/src/os/file_unix.go:132 +0x55
  os/exec.(*Cmd).closeDescriptors()
      /usr/local/go/src/os/exec/exec.go:263 +0x67
  os/exec.(*Cmd).Wait()
      /usr/local/go/src/os/exec/exec.go:448 +0x2b8
  github.com/derekparker/delve/cmd/dlv.TestBuild.func1()
      /home/kbuilder/go/src/github.com/derekparker/delve/cmd/dlv/dlv_test.go:82 +0x8e
  github.com/derekparker/delve/cmd/dlv.TestBuild()
      /home/kbuilder/go/src/github.com/derekparker/delve/cmd/dlv/dlv_test.go:104 +0xb6a
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:657 +0x107

Previous read at 0x00c4201379a0 by goroutine 12:
  os.(*File).Read()
      /usr/local/go/src/os/file.go:98 +0x70
  bufio.(*Scanner).Scan()
      /usr/local/go/src/bufio/scan.go:207 +0x539
  github.com/derekparker/delve/cmd/dlv.TestBuild.func2()
      /home/kbuilder/go/src/github.com/derekparker/delve/cmd/dlv/dlv_test.go:93 +0x38

Change-Id: I09d188dbf964fe4af0b33b6a8fcfe51396176b7e

* 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

According to https://golang.org/cmd/go/#hdr-Test_packages
service_test is more appropriate becuase this directory contains
no non-test code and the intention is to compile these *_test.go
files as a separate package and link/run with the main test package.

- 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

GdbserverProcess does its cleanup in Detach we need to always call
that function.

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

Fixes #783

* 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

* cmd/dlv: fall back to go env GOPATH when GOPATH envvar is unset.

Since Go 1.8, GOPATH environment variable has a default value if the
environment variable is unset so not setting GOPATH is perfectly ok.
Depend on `go env` command to query Go related environment variable.

* build: update references to moved packages