[MINOR] add a new CLF log format

Appending the "clf" word after "option httplog" turns the HTTP log
format into a CLF format, more suited for certain tools.
diff --git a/include/types/proxy.h b/include/types/proxy.h
index 43f31a6..c9bd0a9 100644
--- a/include/types/proxy.h
+++ b/include/types/proxy.h
@@ -120,6 +120,7 @@
 #define PR_O2_SMARTACC 	0x00000080      /* don't immediately ACK request after accept */
 #define PR_O2_SMARTCON 	0x00000100      /* don't immediately send empty ACK after connect */
 #define PR_O2_RDPC_PRST	0x00000200      /* Actvate rdp cookie analyser */
+#define PR_O2_CLFLOG	0x00000400      /* log into clf format */
 
 /* This structure is used to apply fast weighted round robin on a server group */
 struct fwrr_group {