Fixes #586, the error was not due to the values being compared, but to the
comparison function itself.

See http://projects.scipy.org/numpy/ticket/1684 if you're curious.

tests.

tensor/test_basic:T_scalarfromtensor.test0 which was already a known failure

This should unbreak GPU shared variables, broken after [c4a975e14f7c].

Instead of suppressing calls to free after closing the cuda context, delay closing the cuda context until all calls to free have been made. Might not be *quite* as performant, but feels perhaps a little cleaner.

Track whether there is a gpu context active; if not, don't try to free memory. Note that trying to free the memory and then just not displaying the error doesn't work, since the act of trying to free the memory creates a new gpu context.

None is almost like False, except it is OK do downcast a Python float to
a scalar floatX array. Other specialized case might be added later.

Change all theanorc code blocks in docs to use the 'cfg' Pygments filter which is designed for this.