* 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.

- made GoroutineStacktrace a method of struct G
- made stacktrace a method of StackIterator
- renamed StackIterator to stackIterator
- factored out logic to obtain a stackIterator from a goroutine that's
used by both (*G).Stacktrace and by (*G).UserCurrent

It is sometimes impossible to convert an EvalScope immediately after
starting the program but disassembly can still proceed.

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/

BreakpointInfo variables were always evaluated on CurrentThread
instead of the thread that triggered the breakpoint.

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)

Moved the code in testvariables2 and testvariables4 into
testvariables3, renamed testvariables3 into testvariables2

- 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

Past the maximum recursion depth maps shouldn't be loaded at all,
adding map children and not loading them breaks assumptions in
the prettyprinter.

Fixes #406

Fixes #370.

Mainly just cleans up the code in cmd/dlv/main.go

Fixes #355

Fixes #378

Fixes #370.

This patch modifies the `step` command to step to the next source line,
stepping into any function encountered along the way.

Fixes #360

Typedefs that resolve to slices are not recorded in DWARF as typedefs
but instead as structs in a way that there is no way to know they
are really slices using debug/dwarf.
Using golang.org/x/debug/dwarf instead this problem is solved and
as a bonus some types are printed with a nicer names: (struct string
→ string, struct []int → []int, etc)

 Fixes #356 and #293

Backend only, no UI

Implements #120 (partial)

Fixes #198.

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).

Next sets its temporary breakpoints with the condition that they
must only activate on the current goroutine, and then calls Continue
When Continue encounters a temporary breakpoint it clears all
the breakpoint.

User visible changes: breakpoints that get hit while executing Next
are not ignored.

This commit does not implement full conditional breakpoints
functionality, the only condition that can be set is on the
goroutine id.

Fixes race conditions in Next affecting TestNextConcurrent.

Fixes #320

Go1.6 changed the behaviour of go/constants.

The concrete type of an interface only contains the abbreviated
package name, we must construct a map from package names to package
paths to be able to resolve the concrete type of an interface.

It's was implemented unintentionally and the unintentional
implementation doesn't work and causes a crash.

supported: len, cap, imag, real, complex