Doc clarification and skip flake8 tests on auto saved file

[BUG] in python code and tests fix

Checks compiledir flag for prohibited characters. Fixes #3711

typo in bn.py documentation

Assorted Python 3 fixes

Add TypedListConstant, this fix an optimization warning.

Enable cudnn by default when avaialable in the new back-end

* use Python 2/3 compatible syntax for print;
* use range instead of xrange (creating a list of 100..1000 ints in Python 2 is not a big deal)

Fix Python3 regression in ``pydotprint``

  In Python3 ``map`` returns a map-object (and not a list). This makes the check
  introduced in #3057 fail with "TypeError: unorderable types: map() < list()"

Fix fallback in BLAS detection

Cap memory preallocation to 98% of the total.

set_subtensor GPU realizations