[recursive] handling of code versioning for ops like Elemwise, CAReduce, etc.

Changed the default cache version of Op to ().

Added c_code_cache_version() functions to many Ops that were using the default
before.

scalar/basic.  There is also a cast function, which is used in the grad() of ops
that might upcast their arguments, to downcast the corresponding gradients.

types.

the deprecation warning on startup.

problem.

complex->real is forbidden by the cast() function.

Message.

bumped version numbers on Elemwise and CAReduce.  Not sure why it was necessary, but it fixed my problem. Probably something got changed before and versions werent raised.

makes it play nicer with the new rule that update values must have the same type
as their shared vars.

An alternative fix to several tests would have been to implement a
Tensor->Scalar cast, but I didn't do that because it's nice to just use Tensors.

Reason being there is a problem with the way we deal with strict.  Strictness
requires that a value has exactly the right type, but non-strictness implies
just about any kind of casting including in-exact casting.  What I would like
the default to be is something that means casting is ok as long as it is exact.

had been upcast.  I did this for add, sub, div.  Mul looked tricky so I
didn't do it.

function.  This corresponds to what is already in theano.tensor.

when initializing a shared variable with a value of 0 because subsequent
floating-point assignments will be silently downcasted to 0.  At the same time,
it is slightly more annoying when it comes to float32 vs. float64 differences.