Fix align

Issue #783: python3 compatible - remove relative imports.

Lazy config default value

Fix a test when g++ is not available.

Add triangle/nonzero functions

Try to fix the problem that depending of the inputs strides, the outputs strides of dimensions of size 1 get strides that make it considered not aligned by the PyArray_ALIGNED macro.

We want to have it evaluated only if the config value get used. Otherwise, this will trigger compilation at import time for a following commit.

We call it only if the user didn't provide a value.

This is one of the trickier relative to absolute convertions.  Some
of the initialization code had to be moved from tensor subpackage to
the main theano __init__.py in order to work around a circular dependency.

Update comment after code review.