lang/expect: install example scripts and manpages in the proper location

This commit changes the location of the example scripts and manpages. They are
now installed in the proper PREFIX/bin and PREFIX/man/man1 - so they are in
path and reachable by man(1) - and are renamed with an expect_ prefix to avoid
conflicts due to their common names.

A pkg-message has been added to notify users of this change. Portrevision has
been bumped.

PR: 232732 (based on)
Submitted by: Walter Schwarzenfeld <w.schwarzenfeld@utanet.at>
Reported by: Dennis Clarke <dclarke@blastwave.org>