run-tests: make --debug run in the temporary test directory

tests/run-tests.py

@@ -638,7 +638,7 b' def run(cmd, wd, options, replacements):'
     Return a tuple (exitcode, output).  output is None in debug mode."""
     # TODO: Use subprocess.Popen if we're running on Python 2.4
     if options.debug:
-        proc = subprocess.Popen(cmd, shell=True)
+        proc = subprocess.Popen(cmd, shell=True, cwd=wd)
         ret = proc.wait()
         return (ret, None)