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.