Using better time-stamp format for specifying the cutoff date for listing sequences
(before or since the date) with --onlyShow. The date format is now:
[CC]YYMMDD[-hh[mm[ss]]] - which gives more terse options for
specifying the date than before, plus it is easier to read.
The older syntax for specifying the date is still quietly supported, but no
longer listed in the help output.
Also fixed two minor bugs with how the --onlyShow feature was working.
1) When using --onlyShow, it was incorrectly listing shots in reverse alphabetical order.
2) The cutoff time was supposed to INCLUDE files up-to-and-including (or including-and-after) the
date specified, but the test was omitting sequences whose times matched exactly instead of including them.