bookmarks: add appropriate locking (issue1691)
- make updates of bookmark state locked and atomic
- wrap commit so that commit and bookmarks happen under the same lock
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
See http://www.selenic.com/mercurial/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.