profiling bug understood

[Matthew Fluet]

I think I've groked all of the profiling bug info.  In response to the old
signal handling posts, the current version of the register allocator
doesn't do anything special for %esp; it's treated as a gpr, except at
foreign function calls.  It is, however, the last register to be used, so
it's only used as gpr when there is a fair amount of register pressure,
usually during a long allocatio block.  gcState.stackTop and
gcState.frontier are cached in %edi and $esi

> Matt, if there is anything else you would like to change in the gmon.out file
> format, tell me and I'll put that in.

I don't have any other particular requirements.  If you want to drop some
of the extraneous header info, that's fine with me.