cext: make revlog.c PY_SSIZE_T_CLEAN
Without this, Python 3.8 emits a deprecation warning, as using
int for # values is deprecated. Many existing modules use
PY_SSIZE_T_CLEAN, so this shouldn't be contentious.
I audited the file for all # formatters and verified we are
using Py_ssize_t everywhere now.
Differential Revision: https://phab.mercurial-scm.org/D6196
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install::
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing::
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.