TST: This test currently fails.

Fix to follow immediately :-)
BF: Take care of sign-reversal in rotation matrix calculation.
BF: Calculation of eigen-vectors was confused by sign reversal.

This should fix this. No other side effects, as far as I could tell.
RF: Reorder the function a bit to short-circuit. Use broadcasting.
Added piesno
Added tests
add positivity constrain on the propagator
cleaned init
corrected typos
shore matrix G --> shore matrix positive constraint
Changed tests + small fixes
Changed tests to work with optimal quantile value instead of median
Fixed typo.
Add flag for the positive_constraint
auto pep8
Merge branch 'nipy-dipy-master' into piesno
Merge pull request #334 from arokem/fix_vec2vec

Fix vec2vec
TST: Make travis look at test coverage.
Merge pull request #338 from maurozucchelli/positive_constrain

Add positivity constraint on the propagator
BF: Be explicit.