Improve debug info to show function arguments in stack traces

[aykevl]

Improve debug information (see commit). Also, implement comparing channel values (found while working on this).

This commit adds debug info to function arguments, so that in many cases
you can see them when compiling with less optimizations enabled.
Unfortunately, due to the way Go SSA works, it is hard to preserve them
in many cases.
Local variables are not yet saved.

Also, change the language type to C, to make sure lldb shows function
arguments. The previous language was Modula 3, apparently due to a
off-by-one error somewhere.

[aykevl]

This was very useful while working on #347. It allows inspection of arguments in stack traces, even the internals of map objects for example (they are implemented as *runtime.hashmap and should be treated as pointers in the debugger).

[deadprogram]

Good progress! Now merging.