Initial changes to support Mariadb backend.

[mfang90739]

Running relational_db_testing on top of these changes, the following error is seen:

sqlalchemy.exc.OperationalError: (pymysql.err.OperationalError) (1005, 'Can't create table sdo.test3_object_prop_name (errno: 150 "Foreign key constraint is incorrectly formed")')
[SQL:
CREATE TABLE sdo.test3_object_prop_name (
id VARCHAR(255),
name TEXT NOT NULL,
integer_value INTEGER,
float_value FLOAT,
string_value TEXT,
UNIQUE (id, name),
FOREIGN KEY(id) REFERENCES sdo.test3_object (id) ON DELETE CASCADE
)

[mfang90739]

Just updated MariaDB and SQLite backends to use the revised sql-type methods and new reg-ex constraints. The development for both backends is still work-in-progress, see attached log files for the immediate problems seen with each backend:
mariadb.log
sqlite.log