Require at least c-ares 1.5.0 when configuring.

Require at least c-ares 1.5.0 when configuring.

That way, if you have an older version, we fail at configure time, with
what should be a message indicating that your c-ares is too old, rather
than at compile time, with what might provoke users to ask "what am I
doing wrong?" or "what do I need to fix?" or "why is my compile
failing?" or....

Change-Id: I911574c4d90174b6bd074c5ef537557d47b199dc
Reviewed-on: https://code.wireshark.org/review/22752
Petri-Dish: Guy Harris <guy@alum.mit.edu>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>