DVB media addon: Fix debug build.

- Compiling dvb.media_addon with DEBUG on fails with error message:
    generated/objects/haiku/x86/debug_1/add-ons/media/media-add-ons/dvb/
    MediaFormat.o: In function `av_log2_c': /boot/home/Development/haiku-a4/
    generated/build_packages/ffmpeg-0.10.2-r1a4-x86-gcc2-2012-08-30/common/
    include/libavutil/common.h:80: undefined reference to `ff_log2_tab'
    collect2: ld returned 1 exit status"

- Research done to narrow down the solution space:
    - ff_log2_tab is a array that is nowhere needed in the dvb.media_addon
    - ff_log2_tab is defined as an extern array in the ffmpeg header file
      libavutil/common.h
    - ff_log2_tab is used in the inline function av_log2_c (libavutil/common.h)
      which doesn't get optimized away when compiling with debug information
    - MediaFormat.cpp needs only some Codec-IDs from the ffmpeg header file
      avcodec.h

- The following fixes were tried:
    - Trying to eliminate unused debug symbols with compilation
      flag -feliminate-unused-debug-types (see gcc documentation
      http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Debugging-Options.html#Debugging-Options)
      by adding the following lines to UserBuildConfig
          AppendToConfigVar C++FLAGS : HAIKU_TOP src : -feliminate-unused-debug-types : global ;
          AppendToConfigVar CCFLAGS : HAIKU_TOP src : -feliminate-unused-debug-types : global ;
      -> Failed, because flag -feliminate-unused-debug-types is not supported by GCC 2.95.3

    - Trying to eliminate unused debug symbols in the linker stage
      -> This worked, by removing the LINKFLAG "-Xlinker --no-undefined" when
         linking all objects into the dvb.media_addon we are getting our addon
         with debug symbols.

- Final solution:
    - Instead of adding/removing flags, we just add the missing implementation
      for the ff_log2_tab array in MediaFormat.cpp. This -feels- the seems to
      be the cleanest solution as it is more obvious what's goin' on compared
      to hiding the solution in the Jamfile.

Signed-off-by: Colin Günther <coling@gmx.de>
Media Kit: Add workaround for #11018 to MPEG2 video stream decoder test.

The workaround triggers the loading of all media plugins prior to using
methods of class BMediaFormats. Using the function get_next_encoder()
is used because of two facts

1. It is publicly available and thus can be used by 3rd party apps,
   too.
2. It is already available by including BMediaFormats.h, so there is
   no need to include another header for this workaround.

Signed-off-by: Colin Günther <coling@gmx.de>
(cherry picked from commit 80354716fe8b25c81ec45bd96ae36e171228b8a0)
Media Kit: Add workaround for #11018 to MP3 audio stream decoder test.

The workaround triggers the loading of all media plugins prior to using
methods of class BMediaFormats. Using the function get_next_encoder()
is used because of two facts

1. It is publicly available and thus can be used by 3rd party apps,
   too.
2. It is already available by including BMediaFormats.h, so there is
   no need to include another header for this workaround.

Signed-off-by: Colin Günther <coling@gmx.de>
(cherry picked from commit a89b0a4e69f18b2b3b2c2f5615450a5ddac838af)