gtx: link against libtinfo if termlib is seperated

gtx: link against libtinfo if termlib is seperated

If ncurses is built with "./configure --with-termlib=tinfo", gtx fails
to link because of an undefined reference to the LINES symbol which is
then provided by libtinfo.so and not libncurses.so.

If ncurses is present, additionally check whether LINES is provided by
ncurses or tinfo and set $LIB_curses accordingly.

This change is based on a patch provided by Bastian Beischer.

FIXES 134420

Change-Id: I3e29c61405d90d0b850bafe4c51125bef433452b
Reviewed-on: https://gerrit.openafs.org/12760
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>