Revert "Fixed issue #28 — properly update TagField tag instance cache when loading the object to keep everything in sync. Thanks ebartels and carljm for the legwork."

This reverts commit 1e829d499b2f5af73cda183d3edfcf239174fb55.

Conflicts:

	tagging/fields.py
	tagging/tests/models.py
	tagging/tests/tests.py