Loosen regex for attachments. Ensure reply/comment post data is bytes

Hi there.

Some notes on this pull request:

1) I encountered a problem when attempting to submit a reply with an attached file with special characters.  I have therefore loosened the regular expression for recognising attachment lines.
2) While testing, Requests was failing with UnicodeError when dealing with post data with a non-ascii Attachment filename.  This led me to encoding the post data content for replies and comments.
3) To get the tests to run, I needed to rework the test suite to some extent - the URLs of the easter-egg instances seem to have changed, and there no longer appeared to be a General queue, so I've written in queue creation and have tested replies and comments with attachments.
4) I tried to get the tests running for RT 4.2 also, however transaction 'Content' seems to always be empty coming out of the RT API. (This may have something to do with it: http://www.gossamer-threads.com/lists/rt/commit/120042).

Cheers
Stewart