curl_multi_remove_handle() don't block terminating c-ares requests

Added Curl_resolver_kill() for all three resolver modes, which only
blocks when necessary, along with test 1592 to confirm
curl_multi_remove_handle() doesn't block unless it must.

Closes #3428
Fixes #3371

tests/data/Makefile.inc

@@ -5,7 +5,7 @@
 #                            | (__| |_| |  _ <| |___
 #                             \___|\___/|_| \_\_____|
 #
-# Copyright (C) 1998 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
+# Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
 #
 # This software is licensed as described in the file COPYING, which
 # you should have received as part of this distribution. The terms
@@ -179,8 +179,8 @@ test1550 test1551 test1552 test1553 test1554 test1555 test1556 test1557 \
 \
 test1560 test1561 \
 \
-test1590 \
-test1591 \
+test1590 test1591 test1592 \
+\
 test1600 test1601 test1602 test1603 test1604 test1605 test1606 test1607 \
 test1608 test1609 test1620 \
 \

tests/data/test1592

@@ -0,0 +1,37 @@
+<testcase>
+<info>
+<keywords>
+HTTP
+multi
+resolve
+speedcheck
+</keywords>
+</info>
+
+# Client-side
+<client>
+<server>
+none
+</server>
+<tool>
+lib1592
+</tool>
+ <name>
+HTTP request, remove handle while resolving, don't block
+ </name>
+
+ <command>
+http://a-site-never-accessed.example.org/1592
+</command>
+</client>
+
+# Verify data after the test has been "shot"
+<verify>
+<valgrind>
+disable
+</valgrind>
+<errorcode>
+0
+</errorcode>
+</verify>
+</testcase>