- remove unnecessary comments

Cholesky outputs a triangular matrix, so if a general solve is applied to
a cholesky output, then transform it into a triangular solve.

This transformation canonicalizes sandbox linalg ops so that the various
cholesky-related transformations are not confused by a transpose.

Doc, error message

Update to be more consistent with doc.

Fix gh-2210, Join.grad crash with first input dtype being *int*

Documentation : error messages

Try to clarify

Typo + clarification

Update extending_theano tutorial

[BUG] Fix bug introduced yesterday, fix FFT conv optimization and small pydotprint fix.

Adding new superclass for C ops

subgrad documentation moved from tensor to theano.gradient