Revert "For effficiency reasons, avoid recreating NSValueTransformers by recycling instances" because it was causing a bug when two threads accessed the same object, since there is no mechanism for serializing access.  Specifically, it was causing an EXC_BAD_ACCESS while accessing the dateFormatter property.

This reverts commit 11f6dfb1e02279d4705a70bb001a3041f992f90c.