Fix stackcollapse-perf for C++ userland profiling

This fixes handling of function names with '::' involved, which
show up in C++ if you pass the perf script output through
demangling prior to stackcollapse-perf.

Also disables the skipping of non-kernel code -- perf is equally
useful for profiling user applications.
Merge pull request #22 from toddlipcon/master

Fixups for stackcollapse-perf