transactions: avoid late tear-down (issue641)
We use weak references (ugh) to avoid having to manually delete
transaction references out of each call frame when an exception occurs.
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.