BUG: fix reading pre-0.14.1 pickles of containers with one block and dup items

Series, frames and panels that contain only one block can be unpickled
under the assumption that block items correspond to manager items 1-to-1
(as pointed out in #7329).

I still don't have any of darwin/win/32bit platforms at hand, so I
cannot post those pickles.  Also, my linux has a fresher python than
indicated by filenames of existing pickle test data.  I did generate
some data to test the fix, the question is do you want me to upload it?