lazier generation of stack traces
the throwing function was left out!
Revert "the throwing function was left out!"

Oops, turns out the default handler leaves it out too so this was
correct the first time.

This reverts commit f715ecdc335127508b3eed36c20d320f388a375e.
other comments on github
Merge pull request #717 from adamdruppe/exception_speed

lazier generation of stack traces