Pagespec alias apiver

jmtd's pagespec_alias plugin needs to pass along the extra map parameters (like user) in case the underlying match functions will refer to them. Also, getsetup can now generate the right YAML config syntax for example. Maybe these were API changes since the early work on the plugin (though it did already say use IkiWiki '3.00')?

Here's something I haven't tried on github before ... my repo was cloned from joeyh/ikiwiki but got the pagespec_alias branch from jmtd/ikiwiki. I'm creating this pull request _hoping_ it will go to jmtd, but I don't think I'll know until I click this here button. Joey, please forgive the distraction if it goes to the wrong upstream.