namespaces: add bookmarks to the names data structure
This marks the first use of abstracting our different types of named objects
(bookmarks, tags, branches, etc.) and upcoming patches will use this to
simplify logic.
$ hg init
$ touch unknown
$ touch a
$ hg add a
$ hg ci -m "1"
$ touch b
$ hg add b
$ hg ci -m "2"
Should show unknown
$ hg status
? unknown
$ hg revert -r 0 --all
removing b
Should show unknown and b removed
$ hg status
R b
? unknown
Should show a and unknown
$ ls
a
unknown