CURLOPT_HAPROXYPROTOCOL: support the HAProxy PROXY protocol

Add --haproxy-protocol for the command line tool

Closes #2162

tests/data/test1455

@@ -0,0 +1,56 @@
+<testcase>
+<info>
+<keywords>
+HTTP
+HTTP GET
+</keywords>
+</info>
+
+#
+# Server-side
+<reply name="1455">
+<data nocheck=yes>
+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: barkbark
+
+-foo-
+</data>
+</reply>
+
+#
+# Client-side
+<client>
+<server>
+http
+</server>
+<name>
+HTTP GET when PROXY Protocol enabled
+</name>
+<command>
+http://%HOSTIP:%HTTPPORT/1455 --haproxy-protocol --local-port 37756
+</command>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+<strip>
+^User-Agent:.*
+</strip>
+<protocol>
+PROXY TCP4 %CLIENTIP %HOSTIP 37756 %HTTPPORT
+GET /1455 HTTP/1.1
+Host: %HOSTIP:%HTTPPORT
+Accept: */*
+
+</protocol>
+</verify>
+</testcase>