Added support for tinyint in MySQL adapter

Added support for missing tinyint column type in MySQL adapter.

To use tinyint column type, use 'tinyinteger' as type value when
creating or updating a column.

Eg. $this->add_column('table', 'column', 'tinyinteger');

Postgresql has no equivalent for tinyint, so falls back to smallint
type when 'tinyinteger' is used.

MySQL 5.0 documentation for the tinyint column type can be found at
http://dev.mysql.com/doc/refman/5.0/en/integer-types.html
Updated test to check for correct escape characters in returned string
Merge pull request #81 from sweetbee/tinyinteger

Added support for tinyint in MySQL adapter