Make win32 binary gems only support Ruby 1.9

Ruby 1.8 was officially retired on Jun 30, 2013: http://www.ruby-lang.org/en/news/2013/06/30/we-retire-1-8-7/
Version bump for win32 gem repackaging

Attempted fix for https://github.com/codahale/bcrypt-ruby/issues/72
Version bump for 3.1.1 official release
Ignore generated jar files.
Bump rake-compiler version for windows fat binaries with 2.0 support
Add support for 1.8 and 2.0 on Windows, plus x64 support
RC version bump for super fat Windows binaries
Version bump for 3.1.2 final