* Prevent multiple checkouts of the same asset.
This adds a new method to the Asset model, availableForCheckout.
Port getDataTable to use availableForCheckout instead of doing the
check manually.
Fixes Issue #2347
* Use availableForCheckout in categories controller. Also gate the checkin/checkout actions here.
* Use gate and availableForCheckout in manufactuers as well.
Daniel Meltzer
a852c624d3