Some test scripts are excluded in test-check-module-imports.t, because
import-checker.py reports that hgweb and/or hgwebdir of
mercurial.hgweb are not imported in recommended style.

To fix this issues, this patch make python code fragments embedded in
these files import hgweb from mercurial package at first, and refer
hgweb and hgwebdir via imported hgweb.