Remove OS check.
Add watcher base class.
Update Makefile.am and autoreconf.
Refactor existing FSEvents and kqueue watchers to use the watcher base class.
Update ax_cxx_compile_stdcxx_c11 macros to v. 4 (now it correctly fails if C++11 support is not found).
Fix includes so that it builds on FreeBSD 10.0.
Use base watcher class.
Use a Makefile conditional to use the -framework linker flag on OS X.