manifest: Tag gstreamer

```
<pvanhoof> Looks like there is something wrong with gst.h and missing
           files on the buildbots. I checked gstreamer's current master and it
           contains gsttracerutils.h, but in our builds for tracker it seems to
          be missing
<pvanhoof> https://build.gnome.org/continuous/buildmaster/builds/2016/01/16/30/build/log-tracker.txt
<pvanhoof> Sounds to me that if gst.h depends on that file, that this
           is wrong:
           http://cgit.freedesktop.org/gstreamer/gstreamer/tree/gst/Makefile.am#n255
           it should not be in noinst_HEADERS but be installed then
```