Some cleanup of the subprocess docs in 2.7.  Adds a reference to the
subprocess32 project in PyPI for posix users.
whitespace chaps my hide
#15840: make docs consistent by saying operations on closed files raise ValueError.

Patch by Caelyn McAulay.

Neither Caelyn nor I could find any cases in 2.7 or 3.4/5 where an
operation on a closed stream raised IOError; generally the C
implementation have a macro to check for the stream being closed, and
these macros all raised ValueError.  If we find any, a new bug should
be opened.
#1704474: mark refleak test as specific to CPython

Patch by Christian Hudon.
Issue #21245: updated documentation on exception() method and function.
Issue #18566: Clarify unittest setUp, tearDown doc. Patch by Nitika Agarwal.
#18566: Whitespace