check curses-libs by configure

check curses-libs by configure

Presently, the used curses-library are determined by OS.
The leads to a build error when no curses-headers are installed.
Use configure to test if curses.h or ncurses.h is present.
ncurses takes precedence over curses.h.
If neither the curses- nor ncurses-libs are available, do not build
afsmonitor and scout.
A summary at the end of the configure should make this clear to
everyone.
The variable TXLIBS has been renamed to LIB_curses.

(cherry picked from commit 4a6a00d6f45bd0ac94e2eb05adee41552073643a)
Reviewed-on: http://gerrit.openafs.org/3345
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Change-Id: Iea866ca6dfe758d95ef890f0d95e1c38012048b4
Reviewed-on: http://gerrit.openafs.org/4078
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>