Update squish library to compile under Linux

There is a fix in the libsquish repository to make v1.11 compile under
Linux.  http://code.google.com/p/libsquish/  This involves adding an
#include <limits.h> to a couple of files.
Merge pull request #375 from DavidWyand-GG/SquishForLinux

Update squish library to compile under Linux