Merge branch 'branch4.2'

diff --cc docs/releases.rst
index 43c61887cfcbb08cbc7a597fea311e4f4cf25126,21c4e638bb10826dba1cb5954a061cbf57ef7fdd..07366cad5a36d1766c0140176013a22571c80093
--- 1/docs/releases.rst
--- 2/docs/releases.rst
+++ b/docs/releases.rst
@@@ -4,7 -4,7 +4,8 @@@ Release note
  .. toctree::
     :maxdepth: 2
  
 +   releases/next
+    releases/v4.2.1
     releases/v4.2.0
     releases/v4.1.0
     releases/v4.0.2

diff --cc setup.py
Simple merge

diff --cc tornado/test/web_test.py
Simple merge

diff --cc tornado/web.py
Simple merge