[BUGFIX] [#83853220] User#models.borrowable is now joining the borrowable items

Squashed commit of the following:

commit aebb31933899a2d7dbf6b5c3484aa81e7cd31b44
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Wed Dec 3 21:25:17 2014 +0100

    [FIX CI]

commit b0b039067838931e0223466854e2b6a450fb6aa4
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Wed Dec 3 20:54:43 2014 +0100

    [BUGFIX] User#models.borrowable is now joining the borrowable items
Merge branch 'master' into fs_81940714_maintenance_currency_and_amount