x11-toolkits/open-motif*: Don't share cached Xft renditions across display connections

Xft rendition caching added with the fix #1414 won't check whether the
matching rendition was allocated trough a different display connection.
This causes a forked process that creates Motif widgets on a separate
display connection to fail with RenderBadGlyphSet X error as soon as
the parent process closes its display, thus invalidating the associated
Xft font resource.

Obtained from: https://sourceforge.net/p/motif/code/merge-requests/4/