Bug 10272: make CheckReserves respect ReservesControlBranch

Bug 10272: make CheckReserves respect ReservesControlBranch

CheckReserves was using the CircControl system preference to determine what
patrons an item can fill a hold for. It should be using ReservesControlBranch
instead.

Test Plan:
1) Set ReservesControlBranch to "item's home library".

2) Create an item at Library A, place holds for it for patrons at
   Library B, Library C, and Library A in that order,
   for pickup at the patrons home library.

3) Make sure the holds policy for Library A is set to
   Hold Policy = "From home library" and
   Return Policy = "Item returns home".

   Make sure the holds policies for the other libraries are set to
   Hold Policy = "From any library".

4) Check the item in at Library C, the hold for the patron at Library B
   should pop up, even though it's in violation of the circulation rules.
   Don't click the confirm button!

5) Apply this patch, and reload the page,
   now the hold listed should be for the last hold,
   the hold for the patron at Library A, which is correct.

This patch adds the subroutine C4::Reserves::GetReservesControlBranch as
an equivilent to C4::Circulation::_GetCircControlBranch.

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Fixed POD so that arguments and explanation match (C<$item>).
Also tested opac-reserves.pl for regressions.
Passes all tests, QA script, and Reserves.t.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>