Merge branch 'single_query_playcounts'

Merge branch 'single_query_playcounts'

* single_query_playcounts:
  changed: use specialised dropIndex function call for dropping indexes.
  added: specialised dropIndex function for managing the difference between DROP INDEX calls on sqlite and mysql.
  switch to mysql-compatible DROP INDEX statements, and alter sqlite3 db layer so that it converts these to sqlite-friendly statements
  remove the IF EXISTS from the DROP INDEX - mysql doesn't support it
  remote old pre-addons xml import code that wasn't ever going to work
  fix grammar in comments
  speed up retrieval of library info when browsing by file
  update comment with note regarding items in a folder with content set that aren't yet in the db
  add an extra column to the video database with the parent path id to allow faster lookup of items by folder
  change AddPath so it checks for a previously existing path and make it public
  make sure paths with content set are imported from xml prior to importing media, ensuring we can set the basepath correctly
  use a single query for retrieving playcounts to speed up file listings

Conflicts:
	xbmc/video/windows/GUIWindowVideoNav.cpp