Add MX::RC prereq to Makefile.PL
Make region_name accept undef
Make group_name accept undef
Merge pull request #16 from EtienneM/master

group_name can be undef
Drop our explicit "use" statement of related classes

The classes will be loaded the first time an accessor of theirs is called, so
we don't need to do it here.
Add UserData to run_instances for test purposes
Permit associate_address in VPC (RT#82139)
Prepare 0.23
Merge branch 'master' into topic/related-classes