Starting a small framework for doing regression testing with larger

traces and more complex Bro configurations.

That's "Type 2" in the terminology of
http://www-new.bro-ids.org/devel/projects/testing.html

This leverages btest as well and will replace the set of scripts that
the old private test-suite is using. It can accomodate tests with both
public and private traces.

This is a checkpoint commmit, not much there yet in terms of actual
testing. Also still need to figure out a mechanmism to allow for
different baselines based on which branch we're testing.

testing/external/scripts/test.skeleton

@@ -0,0 +1,2 @@
+@TEST-EXEC: bro -r $TRACES/trace.pcap mt
+@TEST-EXEC: for i in *.log; do btest-diff $i; done