Consolidate the occurrances of the prime used as the multiplier when hashing
to a single #define instead of having several copies in several files.

This excludes the Modules/ tree (datetime and expat both have a copy
for their own purposes with no need for it to be the same).
diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
index b10cb5d..8249e5f 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -881,7 +881,7 @@
     p = (unsigned char *) a->ob_sval;
     x = *p << 7;
     while (--len >= 0)
-        x = (1000003*x) ^ *p++;
+        x = (_PyHASH_MULTIPLIER*x) ^ *p++;
     x ^= Py_SIZE(a);
     if (x == -1)
         x = -2;