avoid modifying array as iterating through it

jsvn

@@ -754,7 +754,7 @@ def lockable(argv, svn, out):
     return RET_OK
 
 def diff(argv, svn, out):
-    doing_summarize = False
+    doing_summarize = '--summarize' in argv
     for i, v in enumerate(argv):
         m = re.match('(.*?)(\.\.\.?)(.*)$', v)
         if m is not None:
@@ -775,8 +775,7 @@ def diff(argv, svn, out):
                     return RET_ERR
                 url1 += '@%d' % r
             argv = argv[:i] + [url1, url2] + argv[i + 1:]
-        if v == '--summarize':
-            doing_summarize = True
+            break
     pout = Popen([svn] + argv, stdout=PIPE).stdout
     for line in iter(pout.readline, ''):
         if doing_summarize: