Additional fixes for Converter.

* last_error implemented and mostly working
* primitive_errinfo implemented; mostly working but not 100% match
* More error cases handled and cleaned up buffer use a bit
More compatibility fixes for transcoding, including crlf logic.

* crlf transcoding modes for Converter
* More complete errors with error bytes, encodings, etc
* Error conditions more consistent with MRI
* Partial unification of encoding flag logic
* Many miscellaneous fixes
Unexclude now-passing Converter tests.
Move XML transliteration into transcoder logic.
Oops fix for encoding of output buffer when none specified.
Suppress .java source lines from final exception in Rake exec.
Better pattern to filter out org.jruby sources from Rake output.