fixed memory leak: CURLOPT_RESOLVE with multi interface

DNS cache entries populated with CURLOPT_RESOLVE were not properly freed
again when done using the multi interface.

Test case 1502 added to verify.

Bug: http://curl.haxx.se/bug/view.cgi?id=3575448
Reported by: Alex Gruz

tests/data/Makefile.am

@@ -93,7 +93,7 @@ test1379 test1380 test1381 test1382 test1383 test1384 test1385 test1386 \
 test1387 test1388 test1389 test1390 test1391 test1392 test1393 \
 test1400 test1401 test1402 test1403 test1404 test1405 test1406 test1407 \
 test1408 test1409 test1410 test1411 test1412 test1413 \
-test1500 test1501 \
+test1500 test1501 test1502 \
 test2000 test2001 test2002 test2003 test2004 test2005 test2006 test2007 \
 test2008 test2009 test2010 test2011 test2012 test2013 test2014 test2015 \
 test2016 test2017 test2018 test2019 test2020 test2021 test2022 \

tests/data/test1502

@@ -0,0 +1,58 @@
+<testcase>
+<info>
+<keywords>
+HTTP
+HTTP GET
+multi
+CURLOPT_RESOLVE
+</keywords>
+</info>
+
+<reply>
+<data>
+HTTP/1.1 200 OK
+Date: Thu, 09 Nov 2010 14:49:00 GMT
+Server: test-server/fake
+Last-Modified: Tue, 13 Jun 2000 12:10:00 GMT
+ETag: "21025-dc7-39462498"
+Accept-Ranges: bytes
+Content-Length: 6
+Connection: close
+Content-Type: text/html
+Funny-head: yesyes
+
+-foo-
+</data>
+</reply>
+
+#
+# Client-side
+<client>
+<server>
+http
+</server>
+<tool>
+lib1502
+</tool>
+ <name>
+HTTP multi with CURLOPT_RESOLVE
+ </name>
+ <command>
+http://google.com:%HTTPPORT/1502 %HTTPPORT %HOSTIP
+</command>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+<strip>
+^User-Agent:.*
+</strip>
+<protocol>
+GET /1502 HTTP/1.1
+Host: google.com:%HTTPPORT
+Accept: */*
+
+</protocol>
+</verify>
+</testcase>