Removed the enforced first non-backslash char in php_class data type.

Otherwise one is not able to define for example a basePeer class outside of the namespace of the model.
Removed constraint/foreign key statements if the table is MyISAM.

Adjusted the MysqlPlatform class that it does not return constraints and foreign key statements if the table engine is MyISAM. Duplicated the tests for mysql with a MyISAM counterpart.
Fixed invalid regex for php_class data type
Adjusted coding style and fixed a innodb vs. myIsam bug in nested set test resulting out of the new distinction between them.
Merge pull request #562 from MArcJ/master

Fixed two bugs: php_class data type and MySQLPlatform MyISAM `foreign key` generation