Bug 16547: Do not display "multi holds" view if only one is selected

Bug 16547: Do not display "multi holds" view if only one is selected

If a hold is selected from the result list, we should let the ability to
select an item-level hold.

Test plan:
I. Detail page
1/ Go to a bibliographic record detail page
2/ Click "Place hold"
3/ Select a patron
=> No change expected, you can select an item

II. Search result, multiple holds
1/ Search for an item with more than one search result
2/ Select several items, click 'Place hold'
3/ Enter a patron card number
=> No change expected, item level holds are not available.

III. Search result, single hold
1/ Search for an item with more than one search result
2/ Select only one item, click 'Place hold'
3/ Enter a patron card number
=> With this patch applied, item level hold is available. The screen is the same
as when you place a hold from the bibliographic record detail page
=> Without this patch you cannot place an item-level hold

QA notes: We could go a bit further and remove the 2 biblionumbers and
biblionumber from hold script, as well as remove the checkMultiHold in
request.tt. We should not have a biblionumbers param that contain a list
of biblionumber separated by '/' but several biblionumber parameters
instead.

QA notes 2: About placerequest.pl, see bug 19618 comment 27.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>