Receive more than one purchase at the same time

This will allow the user to receive more than one purchase order in the same
receiving order. This is only allowed for purchases from the same supplier.

Fixes: http://bugs.async.com.br/show_bug.cgi?id=5673
Change-Id: Idb3da9fef0bd0ca8865efe9f8f105caeb8425b4a