DOC fix docstring typos in cluster/mean_shift_

Leaving the rest of docstring fixes for pull request #2084
Merge pull request #2135 from fhs/meanshift-doc

DOC fix docstring typos in cluster/mean_shift_
FIX unique_labels in corner case
FIX issue with comparable but different dtype
ENH don't allow mix of input multilabel format
ENH simpler check for mix of string and number input
COSMIT better name
Typo
ENH use type_of_target within unique_labels
ENH improve documentation with allowed label types
ENH check that we don't mix number and strings
Flatten label type checking
TST add smoke test for all supported format
COSMIT
PY3K use six.string_type
OPTIM + ENH simplify mix string and number check
FIX bug with indicator format
ENH use a comprehension over imap
ENH optimize KMeans for sparse inputs

In the document clustering example, the speedup is typically between
15× and 150×.
FIX KMeans bug; argsort result apparently not always C-contiguous

It is one my box :(