MINOR: protocol: report the file and line number for binding/listening errors

Binding errors and late socket errors provide no information about
the file and line where the problem occurs. These are all done by
protocol_bind_all() and they only report "Starting proxy blah". Let's
change this a little bit so that:
  - the file name and line number of the faulty bind line is alwas mentioned
  - early binding errors are indicated with "Binding" instead of "Starting".

Now we can for example have this:
  [WARNING]  (18580) : Binding [binderr.cfg:10] for proxy http: cannot bind receiver to device 'eth2' (No such device) [0.0.0.0:1080]
diff --git a/src/protocol.c b/src/protocol.c
index ece2b5b..b33e494 100644
--- a/src/protocol.c
+++ b/src/protocol.c
@@ -81,10 +81,12 @@
 				struct proxy *px = listener->bind_conf->frontend;
 
 				if (lerr & ERR_ALERT)
-					ha_alert("Starting %s %s: %s\n",
+					ha_alert("Binding [%s:%d] for %s %s: %s\n",
+					         listener->bind_conf->file, listener->bind_conf->line,
 						 proxy_type_str(px), px->id, errmsg);
 				else if (lerr & ERR_WARN)
-					ha_warning("Starting %s %s: %s\n",
+					ha_warning("Binding [%s:%d] for %s %s: %s\n",
+					           listener->bind_conf->file, listener->bind_conf->line,
 						   proxy_type_str(px), px->id, errmsg);
 				ha_free(&errmsg);
 			}
@@ -103,10 +105,12 @@
 				struct proxy *px = listener->bind_conf->frontend;
 
 				if (lerr & ERR_ALERT)
-					ha_alert("Starting %s %s: %s\n",
+					ha_alert("Starting [%s:%d] for %s %s: %s\n",
+					         listener->bind_conf->file, listener->bind_conf->line,
 						 proxy_type_str(px), px->id, msg);
 				else if (lerr & ERR_WARN)
-					ha_warning("Starting %s %s: %s\n",
+					ha_warning("Starting [%s:%d] for %s %s: %s\n",
+					           listener->bind_conf->file, listener->bind_conf->line,
 						   proxy_type_str(px), px->id, msg);
 			}
 			if (lerr & ERR_ABORT)