Change utc options to not always override local time

Changed the utc options -u and -U so that they don't always override the
local time options -d and -D when both kinds of options are specified.
Instead, the last type of option (local or utc) specified takes effect (this
is consistent with what happens when both -c and -C options are given).

Also updated the usage message to make it more clear that the BRO_CUT_TIMEFMT
environment variable affects only the -u and -d options.
Add tests for bro-cut
Merge remote-tracking branch 'origin/fastpath'

* origin/fastpath:
  Change utc options to not always override local time
Merge remote-tracking branch 'origin/topic/dnthayer/ticket1209'

* origin/topic/dnthayer/ticket1209:
  Add tests for bro-cut

BIT-1209 #merged
Adding test target to top-level Makefile.