Bug 29279: Don't sort holds ratio numeric columns as 'natural'

Bug 29279: Don't sort holds ratio numeric columns as 'natural'

TO test:
1 - Place a variety of holds on some records
2 - Place more holds on records with low biblionumbers and less on ones with high biblionumbers
3 - Go to Circulation->Holds ratios
4 - Set the ration to 1 and load the report
5 - Sort by the 'Holds ratio' column and note it is incorrect
6 - Apply patch
7 - Confirm sort works correctly on first three columns and call numbers column

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>