Version 4.1.0

Version 4.1.0
 * db-mysql/mysql-{sql,api}.lisp,db-mysql/clsql_mysql.c:
 Latest version of mysqlclient once again changed the C
 structures from which the mysql backend reads data.
 Rather than adding yet another structure definition which
 is enabled by the client version as read by mysql-client-info.lisp,
 the mysql backend has been re-written to ignore in the internal
 C structures. Instead, C wrapper functions for slot access have
 been added to clsql_mysql.c and are used by mysql-sql.lisp to
 access the internals of C structures. This adds a bit of overhead,
 but completely separates the lisp code from trying to keep up
 with the continually changing internal C structure of mysql.
 All tests in the test suite executed correctly with this change.