Change canonical name for BlockIP to BlockUser, since it's been used to block logged...

Change canonical name for BlockIP to BlockUser, since it's been used to block logged-in users as well as IP users since forever.  I double-checked that "BlockIP" still works, in English and other languages.  (I guess this doesn't need a RELEASE-NOTES mention, since it's technically just a localization change?  Or is that too linguistically egalitarian an attitude?)