saveAs gives misleading exceptions #6

using saveAs, I've gotten an HDF5LibraryException even when load works fine.

I made two changes and it fixed the problem:

• adding a .mat to the file name
• creating the directory that I was telling it to save into so that it gets a valid path

There's nothing blocking, but wanted to post an issue because there may be a more helpful way to do error reporting here. Since the HDF5LibraryException seems to be related to a wide variety of possible problems (including not having LD_LIBRARY_PATH set properly), it would be nice for usability to catch it and report a more specific error when possible.