Revert "Revert "use POSIX version of esrerror_r""

This reverts commit ecd6ba76783c7f3cf2bd4bacce760bc37c17007f.

Conflicts:
	os/FStream.cpp

Because it introduced problems on OSX
Use strerror only, simplify
dummy
Merge pull request #54 from breznak/fix_OSX_fstream

Revert "Revert "use POSIX version of esrerror_r""