LP#1180849: test case - ignoring subrequest responses after respond_complete()

This patch adds a regression test for verifying that subrequests
ignore additional responses after respond_complete() is called.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Protect subrequests from post-complete messages

Subrequests (AKA method_lookup()-based API calls) sometimes append
final-lvalue responses to the response list even after respond_complete()
has been called from within the implementation method.  This commit
discards all post-respond_complete values, protecting against extra,
spurious values being returned to the ultimate client.

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>