MINOR: wurfl: indicate in haproxy -vv the wurfl version in use

It also explicitly mentions that the library is the dummy one when it
is detected.

We have this output now :

$ ./haproxy  -vv |grep -i wurfl
Built with WURFL support (dummy library version 1.11.2.100)
diff --git a/src/wurfl.c b/src/wurfl.c
index 75dcf00..5c490f7 100644
--- a/src/wurfl.c
+++ b/src/wurfl.c
@@ -795,6 +795,17 @@
 	return ((ha_wurfl_header_t *)wh)->header_value;
 }
 
+static void ha_wurfl_register_build_options()
+{
+	const char *ver = wurfl_get_api_version();
+	char *ptr = NULL;
+
+	memprintf(&ptr, "Built with WURFL support (%sversion %s)",
+		  strcmp(ver, "1.11.2.100") ? "" : "dummy library ",
+		  ver);
+	hap_register_build_opts(ptr, 1);
+}
+
 REGISTER_POST_CHECK(ha_wurfl_init);
 REGISTER_POST_DEINIT(ha_wurfl_deinit);
-REGISTER_BUILD_OPTS("Built with WURFL support.");
+INITCALL0(STG_REGISTER, ha_wurfl_register_build_options);