Connection validation, auto reconnect

Patch suggested by JR Ruggentaler taken from mailing list from 20. Dec 2012:

> The ERXDatabaseContextDelegate class method databaseContextShouldHandleDatabaseException(EODatabaseContext databaseContext, Throwable throwable) only reconnects to the database if the exception message contains the string "_obtainOpenChannel". The string looks like something from the early WOAdaptor. I changed the code to make the string a property and changed the code to do String.matches() so anyone can configure which messages the ERXDatabaseContextDelegate will reconnect on.