Merge pull request #4881 from jreback/boolean_dup

BUG: bug in getitem with a duplicate index when using where (GH4879)
BUG/ENH: provide better .loc based semantics for float based indicies, continuing not to fallback (related to GH236)
API: stub-implementation of Float64Index (meaning its the 'same' as an Index at this point), related GH263
BUG: make sure that mixed-integer-float is auto-converted to Float64Index
BUG: (GH4860), raise KeyError on indexing with a float (and not a floating index)
TST: test harness for fallback indexing
checkpoint on tests
checkpoint 2
checkpoint 3
checkpoint 4 - slice indexers start
checkpoint 5
checkpoint 6
checkpoint - slicing almost working!
TST: slice indexer test changes in series/frame
BUG: fix partial multi-indexing
FIXED!