run-tests.py: avoid using popen2.Popen4 - use subprocess instead
Use subprocess to emulate Popen4 if available - similar to how it is done in
util.py.
Using popen2 under python 2.6 gives
DeprecationWarning: The popen2 module is deprecated. Use the subprocess module.
adding dir/bar
adding foo
dir/bar
foo
committed changeset 0:d44511117907
adding dir/bar_2
adding foo_2
dir/bar_2
foo_2
committed changeset 1:a85812e0561a
adding a
adding c
removing a
adding b
removing c
adding d
recording removal of a as rename to b (100% similar)