Data.HashMap.Array: Add import list for GHC.Exts
Data.HashMap.Array: Add import list for GHC.Exts

GHC 7.7 now exports fromList/toList for GHC.Exts which conflict with
names defined in this module.

ivan-m/unordered-containers,bgamari/unordered-containers,rimmington/unordered-containers