Add a ucuserid parameter to be used instead of ucuser.
Requested on the API mailing list.
@Halfak also mentioned the following examples:
- list=usercontribs allows for ucusers -- should have something like ucuserids
- prop=revisions allows for rvuser and rvexcludeuser -- should have something like rvuserid and rvexcludeuserid
- list=users allows for ususers -- should have something like ususerids
- meta=globaluserinfo allows for guiuser -- should have something like guiuserid that takes a global user ID
