Index: Tools/scripts/diff.py
===================================================================
--- Tools/scripts/diff.py	(revision 78122)
+++ Tools/scripts/diff.py	(working copy)
@@ -29,8 +29,21 @@
     n = options.lines
     fromfile, tofile = args
 
-    fromdate = time.ctime(os.stat(fromfile).st_mtime)
-    todate = time.ctime(os.stat(tofile).st_mtime)
+    def isomtime(fname):
+        """Return file modification time in RFC 3339 (ISO 8601 compliant) format"""
+        stamp = time.localtime(os.stat(fname).st_mtime)
+
+        # determine UTC offset rounded to minutes
+        # (see http://bugs.python.org/issue7582 for discussion)
+        #   true if file was modified during active DST
+        isdst = stamp.tm_isdst
+        utcoffset = -(time.altzone if (time.daylight and isdst) else time.timezone) // 60
+
+        suffix = "%+03d:%02d" % (utcoffset // 60, abs(utcoffset) % 60)
+        return time.strftime("%Y-%m-%dT%H:%M:%S", stamp) + suffix
+
+    fromdate = isomtime(fromfile)
+    todate = isomtime(tofile)
     fromlines = open(fromfile, 'U').readlines()
     tolines = open(tofile, 'U').readlines()