Minor performance improvement (~3%)
no need to hack begin_db_transaction for JdbcSpec::MySQL, which is removed from activerecord-jdbc-adapter 1.2.1
Merge remote-tracking branch 'aurorafeint/master'
Merge remote-tracking branch 'kir/master'
Merge remote-tracking branch 'origin/master'

Conflicts:
	lib/after_commit.rb
	lib/after_commit/connection_adapters.rb