posixfile_nt: '+' should allow read access.
This fixes unexpected I/O error on committing many files
due to cset:8a53b39cd402 (r4902 in crew).
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.