Marking abandoned branches

Since branch refs are being worked on it would make sense to add an object that marks a branch as being abandoned. The visualization tools would use this to suppress viewing of these branches in their default display.

For example Mozilla has 100s of branches that were abandoned five or more years ago. No point in having them impact a current gitk display.

You would add an abandoned branch marker after the last commit on the branch and adjust the branch ref to point at it. If you want to open the branch again point the branch ref back to the last commit and let git prune remove the marker.

Abandoned branches are common in CVS since it is not distributed. People start working on something in the main repo and then decide it was a bad idea. In the git world these branches usually don't end up in the main repo.