tests: avoid implicit conversion of str to unicode
On Python 2, str.encode('utf-8') implicitly converts the string to unicode and
then back to str.
Using _sys2bytes() ensures that opt is only encoded on Python 3, where opt is
unicode.
Although contrived, before this change, a UnicodeDecodeError could be triggered
on Python 2 when passing non-ascii values to --extra-config-opt.
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.