MEDIUM: patterns: the hdr() pattern is now of type string

This pattern previously was limited to type IP. With the new header
extraction function, it becomes possible to extract strings, so that
the header can be returned as a string. This will not change anything
to existing configs, as string will automatically be converted to IP
when needed. However, new configs will be able to use IPv6 addresses
from headers in stick-tables, as well as stick on any non-IP header
(eg: host, user-agent, ...).
diff --git a/src/proto_http.c b/src/proto_http.c
index da785bb..1906916 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -8489,24 +8489,15 @@
 /*     The code below is dedicated to pattern fetching and matching     */
 /************************************************************************/
 
-/* extract the IP address from the last occurrence of specified header. Note
- * that we should normally first extract the string then convert it to IP,
- * but right now we have all the functions to do this seemlessly, and we will
- * be able to change that later without touching the configuration.
- */
+/* Returns the last occurrence of specified header. */
 static int
-pattern_fetch_hdr_ip(struct proxy *px, struct session *l4, void *l7, int dir,
-                     const struct pattern_arg *arg_p, int arg_i, union pattern_data *data)
+pattern_fetch_hdr(struct proxy *px, struct session *l4, void *l7, int dir,
+		  const struct pattern_arg *arg_p, int arg_i, union pattern_data *data)
 {
 	struct http_txn *txn = l7;
-	const char *vptr;
-	int vlen;
 
-	if (!http_get_hdr(&txn->req, arg_p->data.str.str, arg_p->data.str.len, &txn->hdr_idx, -1, NULL, &vptr, &vlen))
-		return 0;
-
-	data->ip.s_addr = htonl(inetaddr_host_lim(vptr, vptr + vlen));
-	return data->ip.s_addr != 0;
+	return http_get_hdr(&txn->req, arg_p->data.str.str, arg_p->data.str.len, &txn->hdr_idx,
+			    -1, NULL, &data->str.str, &data->str.len);
 }
 
 /*
@@ -8798,7 +8789,7 @@
 /************************************************************************/
 /* Note: must not be declared <const> as its list will be overwritten */
 static struct pattern_fetch_kw_list pattern_fetch_keywords = {{ },{
-	{ "hdr", pattern_fetch_hdr_ip, pattern_arg_str, PATTERN_TYPE_IP, PATTERN_FETCH_REQ },
+	{ "hdr", pattern_fetch_hdr, pattern_arg_str, PATTERN_TYPE_STRING, PATTERN_FETCH_REQ },
 	{ "url_param", pattern_fetch_url_param, pattern_arg_str, PATTERN_TYPE_STRING, PATTERN_FETCH_REQ },
 	{ "cookie", pattern_fetch_cookie, pattern_arg_str, PATTERN_TYPE_STRING, PATTERN_FETCH_REQ },
 	{ "set-cookie", pattern_fetch_set_cookie, pattern_arg_str, PATTERN_TYPE_STRING, PATTERN_FETCH_RTR },