po: Update US English resource

[Ken Sharp]

http://www.winehq.org/pipermail/wine-devel/2011-April/089585.html
(I lost the original mail - along with a bunch of others)

I'm confused as to what the .po files are for.

ise/ize will be correct if the .rc file default is British English. 
Without updating the .po file for US English I don't see how else this 
can be updated - unless it is simply the way it was before with LANG_ 
and SUBLANG_, but then what are the .po files for?  I can't find any 
details in the Wiki and I'm afraid I wasn't around when they were 
introduced...