[glib] gsignal: add a clarification to the docs

[Ryan Lortie <desrt src gnome org>]

commit c476f7cd264ca3c69c002c4bcc1563b17cd976b2
Author: Ryan Lortie <desrt desrt ca>
Date:   Fri Nov 28 16:20:40 2014 -0500

    gsignal: add a clarification to the docs
    
    As evidenced by a mistake that I made recently, this documentation could
    use a little bit of clarification.

 gobject/gsignal.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/gobject/gsignal.c b/gobject/gsignal.c
index be613b6..257fc8d 100644
--- a/gobject/gsignal.c
+++ b/gobject/gsignal.c
@@ -2867,6 +2867,12 @@ g_signal_handlers_disconnect_matched (gpointer         instance,
  * Returns whether there are any handlers connected to @instance for the
  * given signal id and detail.
  *
+ * If @detail is 0 then it will only match handlers that were connected
+ * without detail.  If @detail is non-zero then it will match handlers
+ * connected both without detail and with the given detail.  This is
+ * consistent with how a signal emitted with @detail would be delivered
+ * to those handlers.
+ *
  * One example of when you might use this is when the arguments to the
  * signal are difficult to compute. A class implementor may opt to not
  * emit the signal if no one is attached anyway, thus saving the cost