Replace hex with "0x%x" % ... to fix a trailing 'L' on 32-bit python2

This test was failing because the hash computes values greater than
0x7fffffff, which 32-bit python2 promotes to long, which `hex` formats
with a trailing 'L'. The code that uses it appears to be ok with a
long value, so it's just the test that needs to handle it.

Fix as suggested here:

https://stackoverflow.com/questions/5917203/python-trailing-l-problem

lib/cretonne/meta/constant_hash.py

@@ -20,9 +20,9 @@ def simple_hash(s):
     Compute a primitive hash of a string.
 
     Example:
-        >>> hex(simple_hash("Hello"))
+        >>> "0x%x" % simple_hash("Hello")
         '0x2fa70c01'
-        >>> hex(simple_hash("world"))
+        >>> "0x%x" % simple_hash("world")
         '0x5b0c31d5'
     """
     h = 5381