Make some inconsistent configuration options errors.

This way, if you ask for both setuid and setcap installation of dumpcap,
it will fail, rather than silently (other than a message you might miss)
ignoring the request for setuid installation.  See bug 10246.

Also:

	if you ask for setuid or setcap installation of dumpcap, but
	dumpcap isn't built, it'll let you know that there's nothing to
	make setuid/setcap, and fail;

	if you ask for setcap installation of dumpcap, but setcap wasn't
	found, it'll let you know that it can't install it setcap, and
	fail;

so that it won't silently (other than a message you might miss) ignore
those requests, either.

Change-Id: Ibc01593e59fd1cd1be8c68d8cdacbfdca863efa0
Reviewed-on: https://code.wireshark.org/review/2771
Reviewed-by: Guy Harris <guy@alum.mit.edu>