OptsVisitor: don't try to flatten overlong integer ranges

Prevent mistyped command line options from incurring high memory and CPU
usage at startup. 64K elements in a range should be enough for everyone
(TM).

The OPTS_VISITOR_RANGE_MAX macro is public so that unit tests can
construct corner cases with it.

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
