Update isl to remove platform dependent behavior

isl commit 9e01482 changed an internal comparision function to ensure
consistent results across different platforms. Differences that have
previously observed between Linux and Solaris 10 should disappear with
the updated isl version.
Update isl

isl commit f5ed5dd6 changed the output of one the test cases. We update
isl and the test case to allow CLooG to be compiled with this and later
versions of isl.