This was possible on debug c-ares enabled builds when both CURL_MEMDEBUG
and CARES_MEMDEBUG environment variables were set. Leading to a file handle
leak even when both variables had the same value, and wierd test suite
results when different.

KNOWN_BUGS #25, which happens when a proxy closes the connection when
libcurl has sent CONNECT, as part of an authentication negotiation. Starting
now, libcurl will re-connect accordingly and continue the authentication as
it should.

a fatal bug so we must require 1.3.2 to get flawless functionality with c-ares.

behaviour some versions of IRIX exhibit of committing suicide on big
mallocs instead of just returning a friendly null pointer

fix closing of fd's when limit is reached

when more than FD_SETSIZE file descriptors are open.
This means that if for any reason we are not able to
open more than FD_SETSIZE file descriptors then test
518 should not be run.

test 537 is all about testing libcurl functionality
when the system has nearly exhausted the number of
free file descriptors. Test 537 will try to run with
very few free file descriptors.