small fix.

Documentation improvements

Consistent & correct handling of integers and gradients

-Documentation and implementation of a consistent way of handling gradients and integers
-Type checks that ensure the gradient is always floating point and not an integer
-Type checks that ensure the gradient of an integer is always undefined or 0
-An upgraded version of connection_pattern that provides theano with enough information to answer questions like "is variable x a function of variable y?" accurately

Correct Theanos's tutorial: add cross-references, correct some more typos, improve style a little, correct the logical structure some more

Correct Theano's tutorial: overhaul logic of exposition and integrate exercises and useful info found in CIFAR SC2011 accordingly

fixed an error message