made required attribute XHTML compliant

Signed-off-by: Chirayu Chiripal <chirayu.chiripal@gmail.com>
Feature Request: #1329 Can't rename column with foreign key constraint.

Signed-off-by: Ashutosh Dhundhara <ashutoshdhundhara@yahoo.com>

Removed some irrelevant comments and code.

Signed-off-by: Ashutosh Dhundhara <ashutoshdhundhara@yahoo.com>

Fixed tests.

Signed-off-by: Ashutosh Dhundhara <ashutoshdhundhara@yahoo.com>