Revert "Disable option checks."

This reverts commit 405feb2aa483b7c686b66f78ea82dc675fccc11a.
Implement better alias handling.

When an extension has a 'real_name' attribute, look up that module and
use it as self._module except the 'x6_parse' and 'x6_options' attributes
from the original module (if they are not NULL). The logic in iptables
is that alias modules only use these two for parsing input parameters,
everything else is implemented in the 'real' module.
Only call _update_parameters() in final_check().
Use correct parameters for hashlimit test.
Fix python3 compatibility.

Use dict.items() instead of dict.iteritems().
Add python3 type check workaround.
Merge pull request #126 from ldx/fcheck

Call final_check() before adding/removing a rule.