renamed cscope-last-user-search -> cscope-fuzzy-search-symbol
split the prev-search into a variable: 'cscope-previous-user-search'
Better cscope mouse support

This is partly from

http://sourceforge.net/p/cscope/patches/35/

New features:

- button3 opens a popup menu that runs prompt-less searches
- shift-button3 reruns the last search on the point. This is thus even more
  prompt-less