MPI Ops

One of the mpi tests needs to run a file in the theano file system.

It is now pointed to that file through the theano.__file__ attribute.

mpi_cmp -> mpi_cmps

fix incorrect test `y = x + x` -> `y = x + 1` to match expected output

remove old comments

(these functions moved in a rebase)

I'm currently using os.popen.
I tried using subprocess.Popen without success. Would appreciate tips.

Also removed infer_shape for now

I suspect that this is necessary to hold as an output

Revert "Merge pull request #995 from pascanur/fix_grad_scan_dtype"

This reverts commit 4ecb5a04, reversing
changes made to 8b088c69.

Fix grad scan dtype

Remove debug line following code review.

Doc

Remove a bad unit test

these were caught by my recent input validation pull request, which was
merged before travis could run on it

theano.gradient setup (it was checking that the internal implementation
of grad worked in a specific way, using None values that are not
even allowed anymore)

Fix tests failing with DebugMode.check_preallocated_output=ALL

Add validation of input for some ops