Next attempt to fix the deadlock issue that lead to fd0b77bc11f09106de0636de663bb3d16f7b02c9:

The source of the deadlock problem seems that during DbSource.getConnection() ResourceProperties instances are compared using their equals() method, which is synchronized in Hashtable and can/does lead to deadlocks (see http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6582568).

This commit overwrites equals with an unsynchronized version. Note that this implementation might return a wrong result if one of the two instances is modified during this method call, but at least doesn't throw a ConcurrentModificationException.
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
partly reverted 5f18e3ae2dd62dcd2d6a29840dc0b5ecce76ae07:

switched back to using DbSources as Map keys, as using strings breaks switching databases
using DbSource.switchProperties (which is used in jala.Test)