auto-pausing on verify callback retry

When an application install its own OpenSSL verify callback and
that callback invokes `SSL_set_retry_verify()`, the transfer is
automatically paused and does not progress the connect attempt
any further until unpaused via `curl_easy_pause().

Added test758 to verify.

Original PR by @Natris
Reporting on libcurl mailing list

tests/data/Makefile.am

@@ -108,7 +108,7 @@ test718 test719 test720 test721 test722 test723 test724 test725 test726 \
 test727 test728 test729 test730 test731 test732 test733 test734 test735 \
 test736 test737 test738 test739 test740 test741 test742 test743 test744 \
 test745 test746 test747 test748 test749 test750 test751 test752 test753 \
-test754 test755 test756 test757 \
+test754 test755 test756 test757 test758 \
 test780 test781 test782 test783 test784 test785 test786 test787 test788 \
 test789 test790 test791 test792 test793 test794         test796 test797 \
 \

tests/data/test758

@@ -0,0 +1,53 @@
+<testcase>
+<info>
+<keywords>
+multi
+HTTPS
+</keywords>
+</info>
+
+# Server-side
+<reply>
+<data nocheck="yes">
+HTTP/1.1 200 OK
+Date: Tue, 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: 6007
+Connection: close
+Content-Type: text/html
+Funny-head: yesyes
+
+-foo-
+%repeat[1000 x foobar]%
+</data>
+</reply>
+
+<features>
+OpenSSL
+</features>
+
+# Client-side
+<client>
+<server>
+https
+</server>
+<tool>
+lib%TESTNUMBER
+</tool>
+<name>
+multi_socket interface transfer with callbacks returning error
+</name>
+<command>
+https://localhost:%HTTPSPORT/file%TESTNUMBER
+</command>
+</client>
+
+# Verify data after the test has been "shot"
+<verify>
+<protocol>
+</protocol>
+</verify>
+</testcase>