Make so that the correct Dialect will be selected
Some small api changes: Dialect#alterColumnType, SqlMigration#sql: Seq[String]

Also some Dialect methods take String instead of FieldSymbol
DbTest: Allow to override catalog, schema used by getTables
DbTest: Rename tables. Failing tests don't drop, further tests need new name
Derby now works
Bump scala version to 2.10.2