Add explicit parens around qw() lists as needed
Fix bug in DCC check for momentum dumps

"datestamp" was not a key in the backstop entries, so this check was
not doing anything.  (revealed when testing with date2time updated
to use Chandra::Time, original date2time does not complain on no
input).
Set dark current step-time-checks to use a time tolerance

This seems required for numerical sanity for seconds return from
Chandra::Time.
Add abs() around the new time tolerance check
Merge pull request #87 from sot/fixes_for_conda_perl

Compatibility fixes for more modern Perl (5.18)