Remove some inefficient exception handling

Reported by Greg Barton in Drools 2.x:
http://jira.codehaus.org/browse/DROOLS-487

Using exceptions for flow control can be very inefficient on most modern VMs. This is because exception handling is rarely optimized. Thus it is highly preferable to use conditionals to test for exceptional conditions and avoid them instead of using a try/catch to knowingly trigger them.

I saw some code in org.drools.io.RuleSetReader.resolveSchema() that tested various locations for the xsd file using exceptions for flow control. Attached is a patch that eliminates that with identical functionality.