test: verify the opensocket callback for FTP

test 595: for passive FTP
test 596: for active FTP

tests/data/test596

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+#
+# This test is like 585 but uses active FTP instead of HTTP
+#
+<testcase>
+<info>
+<keywords>
+FTP
+</keywords>
+</info>
+#
+# Server-side
+<reply>
+<data>
+moo
+</data>
+<datacheck>
+[OPEN] counter: 1
+[OPEN] counter: 2
+moo
+[CLOSE] counter: 2
+[CLOSE] counter: 1
+</datacheck>
+</reply>
+
+# Client-side
+<client>
+<server>
+ftp
+</server>
+# tool is what to use instead of 'curl'
+<tool>
+lib585
+</tool>
+
+ <name>
+verify close callbacks with active FTP
+ </name>
+ <command>
+ftp://%HOSTIP:%FTPPORT/596 log/ip596 activeftp
+</command>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+<protocol>
+USER anonymous
+PASS ftp@example.com
+PWD
+EPSV
+TYPE I
+SIZE 596
+RETR 596
+QUIT
+</protocol>
+</verify>
+</testcase>