rtpbasepayload: Implement reconfigure event & renegotiation without subclass

Implement the reconfigure event, also do correct downstream caps negotiation
if the subclass doesn't implementy set_caps.

https://bugzilla.gnome.org/show_bug.cgi?id=725361
po: Update translations
Update .po files
Release 1.3.1
textoverlay: Link unit test with the local version of the library, not an installed one
Back to development
discoverer: Add APIs to simply get installer details for missing plugins

Currently the API is far from optimal and the user has to work around
our badly defined API to simply install missing plugins.

API:
  new:
    gst_discoverer_info_get_missing_elements_installer_details

  deprecated:
    gst_discoverer_info_get_misc
    gst_discoverer_stream_info_get_misc

https://bugzilla.gnome.org/show_bug.cgi?id=720596
Add new unit test binary to .gitignore
tests: fix printf format compiler warning in playback test on win32

https://bugzilla.gnome.org/show_bug.cgi?id=729515
Make X11 detection more precise

Don't be content with just X11/Xlib.h, check for X11/XKBlib.h as well.
This prevents false positives (for example, from partial X11 headers
installed by tcl/tk).

https://bugzilla.gnome.org/show_bug.cgi?id=729513
rtsp: Link to ws2_32 on Windows

Needed for getsockname and setsockopt

https://bugzilla.gnome.org/show_bug.cgi?id=729514
win32: Update defs file

commit 622007e7db7e3d32bf8e04e673e057897b646220 added the function
gst_discoverer_info_get_missing_elements_installer_details (). It needs to be
added to the defs file.
playback-test: Set buffer-size only for non-negative size

https://bugzilla.gnome.org/show_bug.cgi?id=729617
Revert "playback-test: Set buffer-size only for non-negative size"

This reverts commit 07a637e2847d56d0f2b0c0ac9095bf37dd324e26.
examples: fix indentation of playback-test
examples: playback-test: fix crashes when setting buffer-size

playbin's buffer-size property takes a gint, not a gint64,
so only pass the bits expected to the vararg function, or
the terminator might not be found, leading to crashes, esp.
with negative numbers.

Spotted by Ravi Kiran K N <ravi.kiran@samsung.com>

https://bugzilla.gnome.org/show_bug.cgi?id=729617
configure: Use X11 detection macro from common

https://bugzilla.gnome.org/show_bug.cgi?id=729621
oggmux: push eos event when empty pad data

If gst_ogg_mux_queue_pads returns NULL it means we are at EOS, because we get a
NULL buffer and this function never sets bestpad.

https://bugzilla.gnome.org/show_bug.cgi?id=729315
uridecodebin: use downloadbuffer for download buffering

Use the new downloadbuffer element to implement the download buffering
feature

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=680183
videodecoder: Retry setting configuration with modified config

Buffer pool set_config() may return FALSE if requested configuration needed small
changes. Reget the config and try setting it again. This ensure we have a configured
pool if possible.