TST: windows dtype correction
PRF: .shift() speedup: Only pass in c_contiguous arrays to np.roll/take
PRF: Fixed shift speed tests and added consolidated DataFrame shift perf
test
BUG: fix NDFrame.as_blocks() for sparse containers

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.
Merge pull request #6747 from dalejung/quick_shift_fixes

Quick shift fixes
Merge pull request #6748 from immerrr/fix-as-blocks-for-sparse

BUG: fix NDFrame.as_blocks() for sparse containers