Avoid Elemwise fusion for scalar Ops without C implementations

Misc. Dot test and interface fixes

Add handling for non-NumPy types in Shape/Shape_i

This change allows `Shape`/`Shape_i` to handle non-standard `Op` values, like
the `None` and `list` values produced by `NoneType` and `MakeList` `Op`s.

The one drawback to this change is that `theano.scan`, i.e. the `scan` function
exposed by `theano/__init__.py`, shadows the `theano.scan` sub-package.

In other words, modules in the `theano.scan` sub-package cannot be accessed via
the top-level `theano` module object (e.g. `import theano; theano.scan.op.Scan`
won't work).

This is a minor inconvenience, and, since internal library code is generally
expected to import objects directly from the modules in which they're defined,
the appearance of this problem will serve as a welcome warning.

This replaces `theano.tensor.basic.dot` with the old `theano.dot`, removes the latter, and renames `theano.tensor.basic.dot` to `theano.tensor.basic.dense_dot`.

Remove theano.compat and other Python 2.x compatibility code