PRESUBMIT.py: accept variants on the copyright message that are present in the codebase.
PRESUBMIT.py: accept variants on the copyright message that are present in the codebase.

Example files that this makes ok instead of flagging include:
  talk/base/signalthread_unittest.cc
  talk/base/thread_unittest.cc
  webrtc/base/signalthread_unittest.cc
  webrtc/base/thread.cc
  webrtc/base/thread.h
  webrtc/base/thread_unittest.cc

BUG=1027
R=andrew@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/19539006

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 18f41b8eb4da76d6ab4b8c6bf142412dc4a4f4f4

sippet/talk,sippet/talk,sippet/talk,sippet/talk,sippet/talk