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/diff-canonifier

@@ -0,0 +1,5 @@
+#! /usr/bin/env bash
+#
+# Replace anything which looks like timestamps with XXXs.
+
+sed 's/[0-9]\{10\}\.[0-9]\{2,8\}/XXXXXXXXXX.XXXXXX/g'