docs: fix gtk-doc warnings

Move MT safety to main description (it does not belong to Return: or Since:
statement). Add a few missing return docs. Downgrade a normal comment froma doc
comment. Fix a doc header to only contain symbol name.

gst/gstclock.c

@@ -555,7 +555,7 @@ gst_clock_id_unschedule (GstClockID id)
 }
 
 
-/**
+/*
  * GstClock abstract base class implementation
  */
 G_DEFINE_TYPE (GstClock, gst_clock, GST_TYPE_OBJECT);

gst/gstmessage.c

@@ -427,10 +427,10 @@ gst_message_new_warning (GstObject * src, GError * error, const gchar * debug)
  * Create a new info message. The message will make copies of @error and
  * @debug.
  *
- * Returns: The new info message.
- *
  * MT safe.
  *
+ * Returns: The new info message.
+ *
  * Since: 0.10.12
  */
 GstMessage *
@@ -488,10 +488,10 @@ gst_message_new_tag (GstObject * src, GstTagList * tag_list)
  * message with @percent set to 100, which can happen after the pipeline
  * completed prerolling. 
  *
- * Returns: The new buffering message.
- *
  * MT safe.
  *
+ * Returns: The new buffering message.
+ *
  * Since: 0.10.11
  */
 GstMessage *

gst/gstpad.c

@@ -3297,9 +3297,9 @@ no_parent:
  * inside of the parent element.
  * The caller must free this list after use.
  *
- * Returns: a newly allocated #GList of pads, free with g_list_free().
- *
  * Not MT safe.
+ *
+ * Returns: a newly allocated #GList of pads, free with g_list_free().
  * 
  * Deprecated: This function does not ref the pads in the list so that they
  * could become invalid by the time the application accesses them. It's also
@@ -4202,10 +4202,10 @@ gst_pad_chain (GstPad * pad, GstBuffer * buffer)
  * In all cases, success or failure, the caller loses its reference to @list
  * after calling this function.
  *
- * Returns: a #GstFlowReturn from the pad.
- *
  * MT safe.
  *
+ * Returns: a #GstFlowReturn from the pad.
+ *
  * Since: 0.10.24
  */
 GstFlowReturn

gst/gstquery.c

@@ -832,7 +832,7 @@ gst_query_get_structure (GstQuery * query)
 }
 
 /**
- * gst_query_new_seeking (GstFormat *format)
+ * gst_query_new_seeking:
  * @format: the default #GstFormat for the new query
  *
  * Constructs a new query object for querying seeking properties of

gst/gsttask.c

@@ -590,10 +590,10 @@ start_task (GstTask * task)
  * gst_task_set_lock() when going to GST_TASK_STARTED or GST_TASK_PAUSED or
  * this function will return %FALSE.
  *
- * Returns: %TRUE if the state could be changed.
- *
  * MT safe.
  *
+ * Returns: %TRUE if the state could be changed.
+ *
  * Since: 0.10.24
  */
 gboolean