DOC: don't say .loc is "strictly label-based" if it isn't
One pedantic little thing I keep noticing: the docs for .loc say repeatedly that it is "strictly label-based", but it also accepts an array of booleans.  I think it's good for .loc to have accept booleans, but it's misleading and confusing for the docs to say (in bold, no less) that it accepts _only_ labels found in the index, and then immediately contradict themselves by saying it also accepts arrays of booleans.  Booleans aren't labels found in the index.
