Adds ability to propogate exceptions within map

Adds init variable for extension managers to specify whether
or not exceptions are propated up by map or are logged and supressed
Formatting fix

Fixes too many blank lines in test_extension.py
Update docstrings for map exception propagation

Updates docstrings related to map exception propagation
and the history.rst file
Fix doc build with Python 2.6.x

subprocess.check_output was new in Python 2.7.
Use an alternative construct via subprocess.Popen
which works on Python 2.6 as well.
Merge pull request #22 from cyeoh/propogate_exceptions

Propogate exceptions
Merge pull request #23 from dirkmueller/python26x

Fix doc build with Python 2.6.x
fixed a bug in the test for propagating map exceptions

A too-broad except clause caused the test to always pass by trapping the assertion error designed to trigger test failure.
Merge pull request #24 from drocco-007/master

Fixed a bug in the test for propagating map exceptions
prep for 0.10 release

Change-Id: Ifce736e14ac1f6721b2188b4bcb8f78534faffd9
Signed-off-by: Doug Hellmann <doug.hellmann@dreamhost.com>