Modified Transactor to store sqlConnections internally using the name of the DbSource
as Map key, not the DbSource instance. Using the instance as key is both inefficient and
error prone (see fd0b77bc11f09106de0636de663bb3d16f7b02c9).

Additional changes:
- modified getConnection() to check if the DB is oracle. "SELECT 1" is invalid
for Oracle DBs and lead to Helma dropping in-use connections every minute.
- set DbSource name final