Bookmark usability issues

[Stefan Rusek]

After spending some time with bookmarks, I find them a pain to use.
This is mostly due to two issues: some of the more important commands
aren't bookmarks aware and there is no way to reference the
non-bookmarked heads.

Push should know about bookmarks, and provide an option to not push
bookmarked heads. "hg push --exclude-bookmarks" would allow one to
create a bunch of bookmarked branches, but only push the
non-bookmarked branches.

Heads should show what heads are bookmarked. Right now one has to type
"hg bookmarks" then "hg heads" and go back and forth between the
outputs to figure out what is what.

Hgk doesn't know about bookmarks either.

If there is only one non-bookmarked head then there should be an easy
way to refer to it. In order to "hg up" to the non-bookmarked head one
has to do far too much work to find that head before one can update to
it. This makes it hard to rebase the bookmark onto the main head.