Change the compiler to use the new routines. Drop the separation of
small and large values when sending on a channel. Allocate the select
struct on the stack. Remove the old C implementation of channels. Adjust
the garbage collector for the new data structure.
Bring in part of the tracing code, enough for the channel code to call.
Bump the permitted number of allocations in one of the tests in
context_test.go. The difference is that now receiving from a channel
allocates a sudog, which the C code used to simply put on the
stack. This will be somewhat better when we port proc.go.
Reviewed-on: https://go-review.googlesource.com/30714
From-SVN: r240941
