Revert "Merge pull request #346 from omarocegueda/syn_registration"

This reverts commit e63c178c4dadeb635936fcf03daa84f9bf8f63f0, reversing 
changes made to c273fe50bd389184ae069fd5a70187e38f699d4d.

We decided to back off these commits until we had checked the code coverage of
the Cython modules, or timed out doing that.

Discussion here:

https://github.com/nipy/dipy/pull/34