Revert "Use after_commit to reduce multi-version race conditions"

Complex callbacks actually depend on the old behavior, making this change slightly unsafe.
Will be removing multi-versioned keys altogether soon.

This reverts commit 388b4d51c844c91dbc6664733fcf2ff10b1d419d.

Conflicts:

	gemfiles/activerecord_2.3.gemfile.lock
	gemfiles/activerecord_3.0.gemfile.lock
	gemfiles/activerecord_3.1.gemfile.lock
	gemfiles/activerecord_3.2.gemfile.lock