My package gtkhash can now build both against gtk2 and gtk3. I am about
to package the two versions as gtkhash and gtkhash3, but both packages
would share one file, /usr/share/gtkhash/gtkhash.xml.
You can install both packages at the same time, at least here on F15 it
works fine. However it is not allowed by the packaging guidelines:
"Packages must not own files already owned by other packages." 
I wonder if this rule is still needed. I know I'd loose backward
compatibility with older rpm versions, but I don't want make a
gtkhash-common package for only a single file. Can we allow multiple
file ownership, at least when a file comes from the same srpm?