I just pushed a new release of the ffi gem.  If you were already
running master, then there's no difference, except a version number
bump (0.6.3->1.0.0).

Ruby 1.9.2 is now the minimum supported ruby version, and MacOSX with
ruby and libffi built from macports is the only supported[1] platform.

I haven't tested this on other platforms *at all*, but it is likely to
work on Linux, and other, saner unixen.   Only the truly adventurous
would try it on windows[2].

[1] "supported" means if it breaks, I'll help fix it.  Everything
else, someone will need to send patches/github pull requests with
fixes, if it is broken.

[2] Windows will need someone to fix up the callback-on-non-ruby-
thread support.