The try_run function in command/config.py is used to
run a test program as part of configuring an extension
module with "python setup.py config" before running
"python setup.py build". When running the test program,
the current directory is not included in the program
name. So it attempts to run _configtest instead of
./_configtest. This works fine as long as the user has
the current directory in the path. If not, the attempt
to run _configtest fails. The patch adds the current
directory in front of _configtest, so that the program
runs even if the user does not have the current
directory in the path.