Dockerfile to build a working igprof image.
Merge pull request #49 from ktf/docker-file

Dockerfile to build a working igprof image.
Avoid crash in multithreaded programs.

This is needed because apparently unw_backtrace fills the last entry of
the stack array with a 0 in case we are talking about the stacktrace of
a (non-main) thread, resulting in a subsequent crash in childStackNode.