JRuby test explorations

[headius]

Here's some notes from the RubyConf hack session for net-imap on JRuby.

• There's one test currently that hangs the suite: test_starttls_unknown_ca from test_imap.rb. I have not investigated but it hangs with a single thread at 100% apparently doing an SSL socket read over and over.
• assert_local_raise has issues on JRuby similar to those found in TruffleRuby, where setting the backtrace to nil does not cause it to get repopulated by a subsequent raise. Stubbing out the assertion dropped total F+E from 100 to 85.
• The Data classes defined in command_data.rb appear to be losing state. This is probably a continuation of bugs with the specialization of Data to use real fields in JRuby. Subclasses aren't inheriting that field metadata properly so the state is lost.