avoid inlining in appropriate places

avoid inlining in appropriate places

fix problems with caller/callers differences on go tip

There's some minor changes to ensure future go compilers don't
inline important functions, but the major change is making
findPtr and getStack both use Callers.

I don't think I need to use CallersFrames, since the PC of
the caller is fine as long as it's stable for the same
call site.

fixes #7

Merge pull request #3 from flimzy/js

Add support for GopherJS build target