Update whatsnew/2.7.rst, add a few links and fix a couple of XXX.  Also add a paragraph about DeprecationWarnings in cmdline.rst.

Issue 8202 actually caused an unintended behavioural change and was reverted in 2.7 - remove reference from What's New

  - insert commas between entries in del statement
  - left and right shifts were represented as >> and << (respectively); reverse
  - unindent properly after for: else:  or while: else:
  - add parens around the result of an unary operation
  - add parens around negative numbers, to avoid turning (-1)**2 into -1**2.

Documentation correction. urllib2.urlopen.info returns a mimetools.Message instance not HTTPMessage object.