util: initialize md5 and sha1 without using extra global variables

This lets the functions skip the "if _sha1 is None" test on each call.

mercurial/util.py

@@ -20,28 +20,26 b' import imp'
 
 # Python compatibility
 
-_md5 = None
 def md5(s):
-    global _md5
-    if _md5 is None:
         try:
             import hashlib
             _md5 = hashlib.md5
         except ImportError:
             import md5
             _md5 = md5.md5
+    global md5
+    md5 = _md5
     return _md5(s)
 
-_sha1 = None
 def sha1(s):
-    global _sha1
-    if _sha1 is None:
         try:
             import hashlib
             _sha1 = hashlib.sha1
         except ImportError:
             import sha
             _sha1 = sha.sha
+    global sha1
+    sha1 = _sha1
     return _sha1(s)
 
 import subprocess