Spec examples for Property#set_original_value
Spec examples for Property#set_original_value

* I feel like testing plumbing methods makes little sense
  but still makes some. If dkubb agrees that we should
  go for more integration specs instead, I'd not mind
  just removing these

tpitale/dm-core,datamapper/dm-core,engineyard/dm-core,ar-dm/ardm-core,alloy/dm-core,tillsc/dm-core