Needed a way to easily create new ReDBox XML files with unique IDs so that
the alerts harvester doesn't ignore them.  A 'test' flag can now be passed
to the Source scanner which will tell it to revisit input files it's already
seen.  Modified harvest.pl to take a -t switch to turn this on.  Modified
harvest_test to take a -f flag which will make it rebuild the fixtures
(and thus reset the id counts).