Item12364: getting the version info while saving a topic was blowing away the content of the topic. Load the version info via a dummy object instead

git-svn-id: http://svn.foswiki.org/trunk@16443 0b4bb1d4-4e5a-0410-9cc4-b2b747904278
Item11326: the code that adds entries to a subscriber set was attempting to optimise the set each time an entry is added. This is a worst-case O(N^2) process, but guarantees a fast lookup when searching for matches in the set. So there's a comromise here; by skipping the optimisation on the read we accept there may be some suboptimal entries. Optimising when a new webnotify is written redresses the balance somewhat.

git-svn-id: http://svn.foswiki.org/trunk@16444 0b4bb1d4-4e5a-0410-9cc4-b2b747904278