tests: do not change sys.path, it can break loading cext.parsers
When running this tests with run-tests, the prefix would resolve
mercurial.cext to the source tree and the attempt to load
mercurial.cext.parsers would therefore fail since it doesn't exist in
it. With the regular search path from run-tests, it is picked up from
the temporary prefix correctly.
Differential Revision: https://phab.mercurial-scm.org/D4910
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.