Add feature modifier to versions produced from branches

Add feature modifier to versions produced from branches

Certain branches, such as Certified Asterisk, may have a modifier added to
them that specifies the features available in that branch.  For branches, this
modifier is expected to be reflected in the location of the branch in
subversion. For example, a subversion of URL of /certified/branches/1.8.11
would have a feature modifier of 'certified'.  This is slightly different then
how features are determined for tags, where the feature is part of the actual
tag name, e.g., "10.5.0-digiumphones".

In keeping with the nomenclature used for tags, the feature specifier for
branches is translated and placed after the revision numbers.  For the example
given previously, this would result in a branch version of
"Asterisk SVN-branch-1.8.11-cert-rXXXXXX".

git-svn-id: https://origsvn.digium.com/svn/asterisk/certified/branches/1.8.6@368607 65c4cc65-6c06-0410-ace0-fbb531ad65f3