Add stdlib.h include for atol().

This attempts to fix issue #600. `man atol` claims that atol() is in
stdlib.h, which wasn't included yet.
Merge pull request #601 from nico/109fix

Add stdlib.h include for atol().
support Bitrig
cleanup based on comments from martine
ugh, missing #
Exclude Windows as well
use !defined(NOT_PPOLL)
Merge pull request #607 from dajohi/master

Support Bitrig