config.py: Adds proxies() @property function

Since remotedb.py and tar.py both made use of the same code
that determined available proxies, the code has been moved to a
function in config.py and both files have been changed to make use
of this function as a value.
api.py: fixes success assignment in delete_repos()
api.py: fixes byte string output for update_news()
config.py: moves EPREFIX constant to top of file
layman.8.txt: Adds changes to reflect new features in layman
layman.cfg: Adds repo configuration options
reposconf.py: Adds overlay priority value
Various syntax fixes

Fixes to docstring indentation, output messages, and function
definition syntax.
Replaces "subpath" with "branch"

In favor of a more widely used varaible, the subpath variable has
been replaced with branch. In preparation for branch support in
overlay.xml files.

layman.8.txt: An example of an overlay.xml with a branch in it has
been added for users along with pointers to using the variable.
{cvs, tar}.py: Fixes assignment for self.branch

Fixes commit: fix undefined 'subpath', update tests
SHA:0fde69e7ef993c3e5cca925cef35c8c895cfd834
Author: dol-sen <brian.dolbec@gmail.com>
Date: Sat 23 Jul 2011 02:44:26 AM EDT

Fixes commit: removal of xml from the vcs class parameters.
SHA: ba5f0cd5c948bb7a65ab21008c940caf0fbe38e7
Author: Brian Dolbec <brian.dolbec@gmail.com>
Date: Thu 24 Feb 2011 01:49:58 AM EST
darcs.py: Adds module branch support
git.py: Adds module branch support
mercurial.py: Adds module branch support
dbbase.py: closes df file descriptor