Bug 23382: hours_between should match the logic of days_between

Bug 23382: hours_between should match the logic of days_between

The loops for subtraction holiday dates in hours_between and
days_between differed and as such their handling of start and end
boundaries for days also differed.  This patch makes them handle the
boundary days consistently.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>