bookmarks: write bookmarks file deterministically
Bookmarks are internally stored as an unsorted dictionary. Let's at
least write out the bookmarks file in a deterministic order so it is
easier to test, diff, etc.
Differential Revision: https://phab.mercurial-scm.org/D2469
https://bz.mercurial-scm.org/1089
$ hg init
$ mkdir a
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ hg ci -m m a
$ mkdir a b
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ cd b
Relative delete:
$ hg ci -m m ../a
$ cd ..