SConstruct: use new matlab.py tool, clean up.
SConstruct: use new matlab.py tool, clean up.

Update the SConstruct file to use the new matlab.py (ex mex.py).  The SConscript
file was also cleaned up a bit. It now has a '--linux32' option to enforce 32
bit compilation on 64 bit Unix systems with 32 bit Matlab (typically student
computers). Also, instead of copying the mexversion.c file, the Repository()
function is used to add the Matlab "src" directory to the source file search
path.  Finally, some missing CFLAGS were added for OS X.

marcecj/mdirac,marcecj/mdirac,marcecj/mdirac