Close subprocess pipes in the non-UNIX section of run_cgi.

Clears a number of ResourceWarnings in test_httpservers.

Lib/http/server.py

@@ -1131,6 +1131,8 @@ class CGIHTTPRequestHandler(SimpleHTTPRequestHandler):
             self.wfile.write(stdout)
             if stderr:
                 self.log_error('%s', stderr)
+            p.stderr.close()
+            p.stdout.close()
             status = p.returncode
             if status:
                 self.log_error("CGI script exit status %#x", status)