Bug 12886: shelfbrowser script should write headers

Bug 12886: shelfbrowser script should write headers

opac/svc/shelfbrowser.pl does not write http headers.

On a production server, this patch resolves a server internal error
(500):
  Bad header=    <div id="shelfbrowser">

I did not reproduce on my local instance, but this should be fixed.

Test plan:
Verify there is no regression on browsing a shelf (with "en" and translated
templates)

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Passes tests and QA script, no regressions found.

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>