Support for postgresql and optional non-recursive autocomplete

Path for PostgreSQL support. This should not break MySQL but I tested only with PostGreSQL

Optional non-recursive autocomplete. With large graphite setups recursing through all subdirectories can be slow. This path allows to set a configuration parameter to only look at the children of the current level for autocompletion.
Todo: in the webinterface it should automatically lookup the next set after selecting so you can 'walk through' the tree of metrics.