Support for MySQL BIT(M) data type default values

replaces pull request #1842

CMysqlColumnSchema: support for MySQL BIT(M) data type proper default
values.
For example, MySQL (MariaDB) return default value as "b'1'" string, not
as "1", so, this case should be considered especially. See also
http://dev.mysql.com/doc/refman/5.0/en/bit-type.html