Use signal and command to provide the same capability of the custom database backend.

Current custom database backend does 3 things:

 1. Call register_hstore for each connection.
 2. Install hstore contrib for every database created.
 3. Create index for hstore field.

This commit use connection_created to do the first two things. And sqlhstoreindexes command to do the third thing.

Plus this commit also fixed an issue when using south to add an hstore field with a default value.
Fall back to JsonField when using sqlite database.
Adding postgis+hstore DB-backend
Adding support of spatial queries
subclasses gis.backend, and created a backends module
added postgis2.0 creation support using refereningc https://code.djangoproject.com/ticket/16455
fixing geodjango bug #16778 by adding adapter
fixing setup.py
finally fixed 0x00-bug
formatting obsession
added tests, geomanager, geoquery and geoqueryset
updated documentation

and a bit of formatting i forgot
updated to current maintainer
dictionary fields now serialize into json
switched to django-based version detection
Fix the bug that one has to install psycopg2 to use the sqlite database
gt, gte, lt, lte lookup
Work in progress Json dict support.
Add json key-value support. Now we could store numbers, dicts and arrays in HStoreField.
Bugfix for processing normal keys.