test: added POP3 test with dot-prefixed line

Test 815 is disabled for now since libcurl currently doesn't unescape
such lines the way it should. See mail:

http://curl.haxx.se/mail/lib-2011-11/0324.html

tests/data/test815

@@ -0,0 +1,56 @@
+<testcase>
+<info>
+<keywords>
+POP3
+RETR
+</keywords>
+</info>
+
+#
+# Server-side
+<reply>
+<data>
+From: me@somewhere
+To: fake@nowhere
+
+..body with a single dot first
+
+--
+  yours sincerely
+</data>
+<datacheck>
+From: me@somewhere
+To: fake@nowhere
+
+.body with a single dot first
+
+--
+  yours sincerely
+</datacheck>
+</reply>
+
+#
+# Client-side
+<client>
+<server>
+pop3
+</server>
+ <name>
+POP3 RETR with dot-prefixed line
+ </name>
+ <command>
+pop3://%HOSTIP:%POP3PORT/815 -u user:secret
+</command>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+<protocol>
+USER user
+PASS secret
+RETR 815
+QUIT
+</protocol>
+</verify>
+</testcase>