Deleted unnecessary variable

before:
        iso_format = iso_format = {'_data-w2p_datetime_format' : '%Y-%m-%d %H:%M:%S'}

now:
        iso_format = {'_data-w2p_datetime_format' : '%Y-%m-%d %H:%M:%S'}
Merge pull request #473 from omartrinidad/master

Deleted unnecessary variable
Merge pull request #474 from leonelcamara/master

Added an optional render argument to as_trees that if True causes it to ...
typo in a comment
Refactored BaseAdapter delete method - Special case code for sqlite and spatialite should not be in the BaseAdapter it should be in SQLiteAdapter, this should also provide a negligible performance boost in delete operations for most adapters including SQLiteAdapter.