ui: fold readsections into readconfig
readconfig now reads only single files
readconfig takes an optional list of sections
readconfig trusts files we're looking for sections in
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.