freeze: exit(2) in examples, to test exit code

The cython_freeze-generated executable exits with code 1 if something
wrong happens, unless a SystemExit exception occurred, in which case it
returns the value passed to sys.exit().  In order to differentiate
between the two cases, change the two example Cython modules to exit(2).

Demos/freeze/cmath.pyx

@@ -19,6 +19,6 @@ if __name__ == "__main__":
     import sys
     if len(sys.argv) != 2:
         sys.stderr.write("USAGE: %s n\nPrints n!.\n" % sys.argv[0])
-        sys.exit(1)
+        sys.exit(2)
     n, = map(float, sys.argv[1:])
     print factorial(n)

Demos/freeze/combinatorics.pyx

@@ -9,6 +9,6 @@ if __name__ == "__main__":
     import sys
     if len(sys.argv) != 3:
         sys.stderr.write("USAGE: %s n r\nPrints n-choose-r.\n" % sys.argv[0])
-        sys.exit(1)
+        sys.exit(2)
     n, r = map(float, sys.argv[1:])
     print nCr(n, r)