updated ConcatTable so that it works with table inputs as well as tensors

OK, so this one might not be popular.  I see no reason why ConcatTable should fail when the input is a table...  The documentation does say:

"ConcatTable is a container module that applies each member module to the same input Tensor."

However, it's a pretty trivial code change to allow table inputs as well.  I've found lots of applications where I've run into this limitation.

The commit below is pretty simple and I added a unit test for concat table for all code branches.  Please let me know what you think.

FYI: I'm happy to get rid of the assert calls if you think the string comparison is too expensive.
this should be removed in the final version