Bug 10590 - parameterise the limit option

Bug 10590 - parameterise the limit option

The limit option was previously substituted directly into the query. The
previous patch on bug 10590 filters it on input, but there's no reason
not to have it made to work properly in the query for added safety.

To test:

[1] Go to the top checkouts report (http://OPAC/cgi-bin/koha/opac-topissues.pl)
[2] Run the report several times, varying the filters on
    number of results and item type.
[3] Verify the the list of top checkouts appears to be correct.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>