adding 2.3.0 release notes
- Add support for alternate content sources.
fix unit test.
add remaining unit tests.
docstrings.
Merge remote-tracking branch 'origin/mhrivnak-exec-perm' into pulp-2.3
nectar config util.
docstrings.
docstrings.
change to content warehouse.
validate plugin.
first pass at the content sources user guide page.
Don't run tests in the plugins directories on rhel5
Merge pull request #721 from pulp/mhrivnak-23releasenotes

adding 2.3.0 release notes
Merge pulp-2.3 => master, pre-build
Automatic commit of package [pulp] release [2.3.0-1].
Automatic commit of package [pulp-nodes] release [2.3.0-1].
Merge (-s ours) pulp-2.3 => master, post-build
Merge pull request #727 from pulp/barnabycourt-block-plugins-dirs-from-rhel5-test-runner

Don't run tests in the plugins directories on rhel5
correcting the supported OS versions in the install docs