go1.9 no longer needs "linkmode internal" on windows.

Fixes #755
Fixes #477
Fixes #631

* Fix various issues detected by megacheck

I've ran honnef.co/go/tools/cmd/megacheck and fixed a few of the
things that came up there.

* Cleanup using Gogland

Implements #727

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

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.

* dwarf/line: bugfix: not all values of the state machine can be used

According to DWARF Version 3 Section 6.2 "Line Number Information" not
all the values transversed by the line numbers state machine are valid
instructions, only the ones after a "special opcode", after the
standard opcode DW_LNS_copy and the extended opcode
DW_LINE_end_sequence.

DWARF3 describes this by specifying that only the opcodes listed above
"append a row to the matrix".

Additionally the implementation of DW_LNS_const_add_pc was wrong.

Fixes #664

* dwarf/line: fixed test failing with go1.8

* service/test: fix prologue detection tests

The conditions about which function prologue is emitted by the compiler
changed in go1.8, changed the test program so that callme2 will still
have a prologue under go1.8.

* service/test: fix step test

compilation units are linked in a different order under go1.8 so the
code of 'fmt' is no longer located after 'main' in the executable,
changed the tests so that they don't rely on this assumption anymore.

* proc: change runtime.Breakpoint support for go1.8

Before 1.8 it was sufficient to step twice to exit a
runtime.Breakpoint(), but go 1.8 added frame pointer tracking to small
functions making runtime.Breakpoint longer.
This changes runtime.Breakpoint handling in Continue to single step as
many times as are needed to exit runtime.Breakpoint.

* proc/test: fix TestIssue561 for go1.8

This version preserves the order of requests, allows the
client to switch between API versions and introduces a
way to send notifications to the client (see TODO item at:
proc/proc_linux.go:325).

Fixes #523, #571

* tests: update to cope with go1.7 SSA compiler

* de-vendored golang.org/x/debug/dwarf

We need our own tweaked version

* dwarf/debug/dwarf: always use the entry's name attribute

Using the name attribute leads to better type names as well as fixes
inconsistencies between 1.5, 1.6 and 1.7.

* proc: Updated loadInterface to work with go1.7

go1.7 changed the internal representation of types, removing the string
field from runtime._type.
Updated loadInterface to use the new str field.

* service/api: Removed unused fields of service/api.Function

* proc/eval: Set return variable name to input expression

* all: fine-grained control of loadValue for better variable printing

Makes proc.(*Variable).loadValue loading parameters configurable
through one extra argument of type LoadConfig.
This interface is also exposed through the API so clients can control
how much of a variable delve should read.

New API version with better backwards compatibility plus mechanism to
select the API version that a headless instance should use.

Adds service/test/cmd/typecheckrpc.go to type check the RPC interface.

Automatically sets a breakpoint on runtime.startpanic, the function
that gets called by runtime.dopanic when a panic is not recovered.

Implements #317

The go compiler changed and break statements no longer get compiled to
nothing when -N is passed:

https://go-review.googlesource.com/#/c/19848/
https://go-review.googlesource.com/#/c/19854/

Lists all the types defined in the debugged program.

proc.(*Process) methods are not thread safe, multiple clients
connecting simultaneously to a delve server (Issue #383) or a even
a single over-eager client (Issue #408) can easily crash it.
Additionally (Issue #419) calls to client.(*RPCClient).Halt can
crash the server because they can result in calling the function
debug/dwarf.(*Data).Type simultaneously in multiple threads which
will cause it to return incompletely parsed dwarf.Type values.

Fixes #408, #419 (partial)

- Unlike FunctionEntryToFirstLine can skip the prologue on functions
that are defined on a single line, either because they weren't
formatted or because they were autogenerated
- Can skip the prologue on most functions when setting a breakpoint
with the filename:line syntax

Fixes #396

Implements #109 and #120

Implements #368

Fixes #370.

Fixes #355

Fixes #378

Location specifiers starting with '*' can be followed by any
expression supported by the evaluator.
The expression should evaluate to either an integer (which will be
interpreted as an address) or to a function pointer (which will be
dereferenced to get the function's entry point).

packagename.SomeFunction should match
github.com/someuser/packagename.SomeFunction since the former is
the familiar syntax.
To disambiguate between io.SomeFunction and
github.com/someuser/somepackage/io.SomeFunction specify one extra
slash at the start of the location specifier: /io.SomeFunction.

Fixes Issue #296

The new contents of api.Variable are documented in
proc/variables.go.

Implements #243

Instead of trying to be clever and make an 'educated guess' as to where
the flow of control may go next, simple do the more naive, yet correct,
approach of setting a breakpoint everywhere we can in the function and
seeing where we end up. On top of this we were already setting a
breakpoint at the return address and deferred functions, so that remains
the same.

This removes a lot of gnarly, hard to maintain code and takes all the
guesswork out of this command.

Fixes #281

Fixes #275

Prevents a lot of goroutines hanging around, especially when running
tests.

set <variable name> <value>

During process termination we seem to receive notifications of new
threads that die before we can add them, ignore them

stack command: -full flag prints local variables and arguments of all the functions on the stack trace

Original implementation was passing the wrong argument.

Breakpoints, tracepoints, etc.. take a location spec as input. This
patch improves the expressiveness of that API. It allows:

* Breakpoint at line
* Breakpoint at function (handling package / receiver smoothing)
* Breakpoint at address
* Breakpoint at file:line
* Setting breakpoint based off regexp