Simple addition to allow writing of int32 arrays

Modified MatFileWriter.java slightly to include capabilities for writing int32 arrays. Really very simple change. Just copied from other case statement examples changing the types. Seems to work though, can load in matlab R2011b.

Honestly, I don't even know if you or anyone else is working on this anymore, but somehow i ended up with your fork of the code, and made this tiny little addition to fix the exception thrown when you try to write int32 arrays, which is the standard Integer in Java. Not sure why it wasn't there before, or if you care, but hey, maybe someone down the line will be in my position and benefit.