If change is from NULL to NOT NULL, no need to update column and alter in stage 3.
Add a test that will make sure an update statement isn't generated when only change is null -> notNull
Move testNullToNotNullDoesNotUpdate to Mysql5TableDiffSQLTest
Add nodb group to limit tests to those not using a database
Ignore all testdata folders
Omit default UPDATES and non-drop stage3 ALTERs for columns
Merge branch 'ajette-mysql-remove-redundancy'

Adds optimizations and simplifications for mysql5 column diffing, and
adds a "nodb" phpunit group to mysql5 tests to aid in running only non-
database-dependent tests.