Factored out _get_flattener

--HG--
extra : rebase_source : f97be8ab2137de3216baa98d298a1cdea59ef128
Fixed typos in 'unpicklable' attribute
Use SimpleReduceHandler to support encoding and decoding of OrderedDict

--HG--
extra : rebase_source : f613e5e8c1ea0baf1d737353aec53349b8be1d4a
extra : histedit_source : 75a9f14fc4b6664c040eeb5311e18ee0786635a6%2C030200d658d07920863ff57423b354ab855ea981
Update SimpleReduceHandler.restore to better follow the protocol.
Merge pull request #42 from jaraco/ordered-dict

Use SimpleReduceHandler to support encoding and decoding of OrderedDict
Merge pull request #40 from jaraco/extract-get-flattener

Factored out _get_flattener