API: Some cleanup and fixes before 1.13 is released:

API: Some cleanup and fixes before 1.13 is released:
* Fix regression from r37270: prop=categories paging was broken in generator mode.
* Fix drlimit=max, which was broken since r31384
* Use titleToKey() and keyToTitle() on title parts of the continue parameters in prop={links,templatelinks,categories,images}
* Use addQuotes() rather than strencode() in those same modules
* Don't trim message names in ammessages, it's stupid and undocumented
* Add $wgAPI{Meta,Prop,List}Modules to DefaultSettings.php explicitly