Fixes for Windows and Python 2.4

Fixed import error in a sparse test

Minor stuff (PEP8 and typos mostly)

The rephrasing is to avoid using 'type' for class name, given that
'type' has a special meaning in Theano.

Add "filter_variable" mechanism in Type

Jacobian/Hessian

If one of the "then" elements is a TensorType, and the corresponding
element in the "else" branch is a compatible type, or vice versa,
convert it into TensorType, so both have the same Type, and the
output Type can be determined.

This should fix a problem reported by Ian.
[Commit amended to fix problem spotted by Fred]

It should work similarly to filter(), but on symbolic variables,
returning equivalent variables of the current Type if they are
compatible.

The 'remove' method was bugged (it would not remove an item if it was the last
item in the queue).
This commit actually replaces the full custom deque implementation by a subclass
of the original Python 2.4 implementation of deque, as it seems safer than
re-writing everything.

The implementation is also moved to the python25.py file since it is the place
for Python 2.4 compatibility code.

Fixed import crash in optimizations

CCW#37: REVIEW/TEST/DOC theano/sparse/sandbox/sp.py:RemoveO

CCW#37: modified theano.config.mode value under which assertion of application of the optimization is done.