update FFI::MemoryPointer.{read,write}_size_t patch to work with jruby.

Also JRuby FFI seems to be missing read_uint{32,64} so provide those as
well.
also test on jruby 1.9 mode on travis.
JRuby doesn't support real file descriptors, so wait_select is not available.
Merge pull request #53 from ledbettj/jruby

Add support for JRuby