allow multiple setup file types, and support safe parsing

allow multiple setup file types, and support safe parsing

Finally removed the last hardcoding of IkiWiki::Setup::Standard.
Take the first "IkiWiki::Setup::*" in the setup file to define the
setuptype, and remember that type to use in dumping later. (But it can be
overridden using --set, etc.)

Also, support setup file types that are not evaled.