Select kqueue for timer on FreeBSD.
Add FreeBSD to conditional compilation that applies to both FreeBSD and MacOSX.
Fix stack_t.ss_sp type difference for FreeBSD.
Fix file data syncing for FreeBSD.
Support systems without python in /usr/bin (Ex, FreeBSD).
Add FreeBSD build environment settings.
Add FreeBSD into configure host list.

Tested on FreeBSD 9 with following setting in config.mk:
 ALLOW_WARNINGS := 1
 LIBRARY_PATHS += -lrt
 CXX := ccache /usr/local/bin/clang -I/usr/local/include -D__STDC_LIMIT_MACROS