rtspsrc: use new method to get media-type

Use the new method to get the media type of a transport.
matroskamux: Add support for g726 ADPCM

https://bugzilla.gnome.org/show_bug.cgi?id=720995
matroskamux: Error out if ADPCM caps don't contain the layout field
rtpbin: remove unused list of decoders

remove list of decoders, which are already handled by the list of elements.

https://bugzilla.gnome.org/show_bug.cgi?id=719938
osxvideosink: Improve configure check for OSX >= 10.6

https://bugzilla.gnome.org/show_bug.cgi?id=721245
configure: Fix AC_COMPILE_IFELSE usage
Revert "matroskamux: Use the running time for container timestamps, not buffer timestamps"

This reverts commit b3aa8755fe07639f22e4104f4932d769d6c9075a.

We are already using the running-time because they were placed on the
buffers with gst_collect_pads_clip_running_time(). Arguably it would be
better to not modify the incomming buffers but collectpads seems to want
to use absolute timestamps from the buffers for finding the best buffer
(this can be changed with a custom compare function..).
qtmux: respect the HDLR box string format for mov and isomedia

Mov spec says it uses a pascal style string, while isomedia uses
a null terminated one. Store the current atoms flavor into the HDLR
to be able to generate the correct output.

https://bugzilla.gnome.org/show_bug.cgi?id=705982
configure: Include AvailabilityMacros.h for osxvideo check

Otherwise MAC_OS_X_VERSION_MIN_REQUIRED might not be defined
matroskamux: write subtitle codec ID and data at start when known

This avoids issues with writing dummy data first, then having
to come back and write correct data later. Doing so prevents
the muxed stream from being actually streamable.

https://bugzilla.gnome.org/show_bug.cgi?id=712134