screen: make better use of the available space in the titlebar

When the terminal is very narrow, there is little point in showing only
part of the version string -- and chewing off one or two digits from the
version number might even give someone a wrong idea.  The user is better
served with always showing the full filename, as long as it fits in the
available screen width.

This fixes https://savannah.gnu.org/bugs/?47703.
1 file changed