properly bail out from, when using ares.

multiple DNS lookups can run simultaneously faster. The downside is that
resolving the same host name now can be made at once from multiple threads,
but the upside is that threads now don't alwys have to wait for the others'
resolves. Test case 506 updated accordingly.

my_getaddrinfo() has been called (and wait has been set to TRUE), we check
if the name already is resolved and if so don't return wait status to the
parent. This can happen with IP-only names.

NOT free the existing hash entry when we try to add a new one that matches
an existing entry. We now instead free the new one, and make the parent
function use the old entry's struct instead.

Problem tracked down by Bjorn Reese.

Jeff Pohlmeyer fixed.

Curl_is_resolved() function

make sure it set async false even when using ipv6 (made test case 20 fail
before)

build libcurl to use ares for asynch name resolves.

the define accordingly in the hostip.h header to work nicely all over.

way for emacs, and vim users should provide a similar non-polluting style

for a bigger buffer and this is indeed badness for us. Making this work
on both old and new glibc versions require an ugly loop that in its worse
form cause 45 bad loops when using the correct glibc and a non-resolving
host name... :-/

We want a better fix. Badly.

for freeing single dns cache entries

AGGRESIVE_TEST is also defined, as an addition to MALLOCDEBUG. It doesn't
work for multi interface usage and should only be used with careful
consideration.

counter so that the caller needs to decrease that counter when done with
the returned data.

If compiled with MALLOCDEBUG I've added some extra checking that the counter
is decreased before a handle is closed etc.

memory. Avery Fay brought the example code that proved this.

size isn't big enough. For some reason they now return EAGAIN.

Redhat 8 ships with this glibc version.

when it can't lookup the name (at least in some cases) and thus we need
to make an extra check to detect failures.