Restructure FishEye so that svn operations do not occur on the main thread

If we try to cancel an svn operation and the svn server fails to respond, the index thread can get locked up.

An option we have would be to restructure FishEye slightly so that svn operations do not occur on the main thread but an ancilary thread so we can regain control of the main thread if need be.

Workarounds are listed in this knowledge base article.