...to select the single textdomain to extract from the files. It is
not really complete (not knowing about the WML scope of #textdomain,
and assuming textual scope), but sufficient for now. Changed default
string-extraction rules to use --domain. Added #textdomain in
"library" wml files from standard campaigns, in places where it would
be missing should those files be #included from different campaigns,
but mostly so their strings get extracted.
