Bug 17444: Enable exporting by time, not only date

Bug 17444: Enable exporting by time, not only date

Test plan:
1) Apply the patch
2) Edit a biblio
3) run export_records.pl with date time few minutes in the past
for example: --format=xml --record-type=bibs --date="2016-10-14 10:00:05" --filename="koha.xml"
4) look in the file and cofirm that the right record was exported
5) Try the same but with time after the biblio was edited, it shouldn't be exported

Signed-off-by: radiuscz <radek.siman@centrum.cz>
Bug 17444: Follow-up, don't change the name of parameter "date"

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>