CLN: move some functions from tools.merge to core.internals
CLN: calculate & use _ref_locs for unique items as well
Move get_series_dict to DataFrame
Use factorization when grouping ref_locs by block

Python3 complained about FloatBlock being non-comparable with NoneType
internals: import OrderedDict from compat

Fixes py26 tests.
SingleBlockManager: remove slot/property conflict

Py3.3 was complaining about that.
ObjectBlock: fix ref_loc handling bug in convert()
SparseBlock: make sure placement is copied
BlockManager: revert _get_counts & get dtype/ftype counts

Python 2.6 doesn't have Counter
Block, SparseBlock: fix placement initialization
BlockManager: deep copy blocks when doing combine(..., copy=True)
make_block: make placement parameter mandatory
NDFrame: fix as_blocks for SparseDataFrame

SparseBlocks don't consolidate, so previous implementation silently
dropped all but the last blocks for given dtype.

Also, drop the 'columns' kwarg, there's reindex for that.
NDFrame: fix typo in as_blocks