[#6149] ticket:356 Fix select field value splitting

* Fall back to regular splitting if shlex.split raises exception
* Always encode unicode-strings before passing it to shlex (it doesn't work well with unicode)
[#5652]  ticket:325 added attachments info for Allura REST API
[#5652]  ticket:325 fixed discussion_thread_url and tests
[#5652] ticket:357 restore output format for wiki page api