fix issue in return unboxing optimization that would sometimes re-create constants on the heap
fix issue in return unboxing optimization that would sometimes re-create constants on the heap

Ignore-this: ca2a43e120adcef3c783cf2ac7df3295

darcs-hash:8ab28384358a553dbff36a0d47492be5566f10d3

dpwright/jhc,dpwright/jhc,dpwright/jhc,dpwright/jhc