Suggestions now use xapian database when available.

If a embedded fulltext database is present, suggestion will search in it :
 - insensitive case search.
 - search for terms in the middle of the title.
 - xapian will try to complete the last word of the query (as if a '*'
   were added at the end)

include/searcher.h

@@ -61,6 +61,7 @@ class Searcher
               unsigned int resultStart,
               unsigned int resultEnd,
               const bool verbose = false);
+  void suggestions(std::string& search, const bool verbose = false);
   Result* getNextResult();
   void restart_search();
   unsigned int getEstimatedResultCount();