[vala/0.40] gstreamer: Cherry-pick some fixes from 0.42

[Rico Tzschichholz <ricotz src gnome org>]

commit 86f821630248815a7634a7a6b7f02b63e8aa2310
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Mon Sep 17 16:33:38 2018 +0200

    gstreamer: Cherry-pick some fixes from 0.42

 vapi/gstreamer-1.0.vapi      | 2 +-
 vapi/gstreamer-base-1.0.vapi | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/vapi/gstreamer-1.0.vapi b/vapi/gstreamer-1.0.vapi
index 372c306fc..28b55b914 100644
--- a/vapi/gstreamer-1.0.vapi
+++ b/vapi/gstreamer-1.0.vapi
@@ -805,7 +805,7 @@ namespace Gst {
                public void disable_sync_message_emission ();
                public void enable_sync_message_emission ();
                [Version (since = "1.14")]
-               public void get_pollfd (GLib.PollFD fd);
+               public GLib.PollFD get_pollfd ();
                public bool have_pending ();
                public Gst.Message? peek ();
                public Gst.Message? poll (Gst.MessageType events, Gst.ClockTime timeout);
diff --git a/vapi/gstreamer-base-1.0.vapi b/vapi/gstreamer-base-1.0.vapi
index 9a86fe2ec..31d49d51a 100644
--- a/vapi/gstreamer-base-1.0.vapi
+++ b/vapi/gstreamer-base-1.0.vapi
@@ -96,7 +96,7 @@ namespace Gst {
                        [NoWrapper]
                        public virtual bool stop ();
                        [NoWrapper]
-                       public virtual Gst.FlowReturn update_src_caps (Gst.Caps caps, Gst.Caps ret);
+                       public virtual Gst.FlowReturn update_src_caps (Gst.Caps caps, out Gst.Caps ret);
                        [NoAccessorMethod]
                        public uint64 latency { get; set; }
                        [NoAccessorMethod]