contrib/wix/COPYING.rtf

run-tests.py: add TESTDIR to PATH if it differs from RUNTESTDIR

Before this patch, `RUNTESTDIR` is added to `PATH`, but `TESTDIR`
isn't.

This doesn't cause any problems, if `run-tests.py` runs in `tests`
directory of Mercurial source tree. In this case, `RUNTESTDIR` should
be equal to `TESTDIR`.

On the other hand, if `run-tests.py` runs in `tests` of third party
tools, commands in that directory should be executed with explicit
`$TESTDIR/` prefix in `*.t` test scripts. This isn't suitable for the
policy "drop explicit $TESTDIR from executables" of Mercurial itself
(see 4d2b9b304ad0).

BTW, 4d2b9b304ad0 describes that "$TESTDIR is added to the path" even
though `TESTDIR` isn't added to `PATH` exactly speaking, because
`TESTDIR` and `RUNTESTDIR` weren't yet distinguished from each other
at that time.

This is a one of preparations for issue4677.

(binary:application/rtf)