We need a better name for this feature.

But basically, this allows for creating kde-project repository-wide
"branch groups". For instance, you could list the git branch to use for
the "stable Qt/KDE 4" release/maintenance branch, the "new development
Qt/KDE 4" development branch (typically master, but that has been
changing), and the "upcoming next major release" branch (for us, this
means 'frameworks' sometimes, means 'master' sometimes, other modules
may have different ideas).

By using the 'branch-group' option (which remains to be further
documented) you can say that you want to defer to the metadata about the
repository branches stored in
kde-build-metadata/logical-module-structure. kdesrc-build should even
track branches for you as they are updated by the Release Team, if you
simply want to hang out on stable but compile your own stuff.

Note that this support requires Perl's JSON module (which should come
with Perl 5.14 if I understand it right, but you probably want to
install JSON::XS from CPAN). JSON support is only required for this
feature, it is not a new overall dependency.

See also: http://community.kde.org/Infrastructure/Project_Metadata