bug fix for issue #3526

Some of the pairwise distances do not support the additional `squared` parameter. I suggest using `sqeuclidian` and such whenever this is required.
bug fix for t-SNE (issue #3526) with new inputs

New fix following the discussion on the previous pull request. Thanks to @jnothman,  @mblondel and others ..
Remove trailing '\' and add test
Describe default metric
Merge pull request #3786 from AlexanderFabisch/tsne_fix

Fix t-SNE with "non-squarable" metric