Fix nftw failure (E_INVAL) on FreeBSD.
Fix dprintf compile error on FreeBSD.
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 steps:
 CXX=clang ./configure
 # edit config.mk to add "ALLOW_WARNINGS := 1"
 gmake