[MEDIUM] New option http_proxy

Hello,

You will find attached an updated release of previously submitted patch.
It polish some part and extend ACL engine to match IP and PORT parsed in
HTTP request. (and take care of comments made by Willy ! ;))

Best regards,
Alexandre
diff --git a/examples/option-http_proxy.cfg b/examples/option-http_proxy.cfg
new file mode 100644
index 0000000..8f73c3b
--- /dev/null
+++ b/examples/option-http_proxy.cfg
@@ -0,0 +1,53 @@
+#
+# demo config for Proxy mode
+# 
+
+global
+        maxconn         20000
+	ulimit-n	16384
+        log             127.0.0.1 local0
+        uid             200
+        gid             200
+        chroot          /var/empty
+	nbproc		4
+        daemon
+
+frontend test-proxy
+	bind		192.168.200.10:8080
+        mode            http
+        log             global
+        option          httplog
+        option          dontlognull
+        option          httpclose
+        option          nolinger
+        option          http_proxy
+        maxconn         8000
+        clitimeout      30000
+
+	# layer3: Valid users
+	acl allow_host src 192.168.200.150/32
+	block if !allow_host
+
+	# layer7: prevent private network relaying
+	acl forbidden_dst url_ip 192.168.0.0/24
+	acl forbidden_dst url_ip 172.16.0.0/12
+	acl forbidden_dst url_ip 10.0.0.0/8
+	block if forbidden_dst
+
+	default_backend test-proxy-srv
+
+
+backend test-proxy-srv
+	mode            http
+	contimeout      5000
+	srvtimeout      5000
+	retries         2
+	option          nolinger
+	option          http_proxy
+
+	# layer7: Only GET method is valid
+	acl valid_method        method GET
+	block if !valid_method
+
+	# layer7: protect bad reply
+	rspdeny ^Content-Type:[\ ]*audio/mp3