Merge mp3 support from Orphis' old FFMPEG code.

Conflicts:
	CMakeLists.txt
	Core/HLE/sceAudio.cpp
	Core/HLE/sceMp3.cpp
	Core/HLE/sceMpeg.cpp
Uncomment some unused stack-corrupting code from sceMp3Decode. Update ffmpeg.
Fix sceMp3 build without USE_FFMPEG
Fix crash in mp3 reading.
Merge pull request #1786 from unknownbrackets/mp3-support

Fix crash in mp3 reading
Get mp3 sample rate and channels from FFMPEG instead of trying to detect ourselves.
VERBOSE a log statement
Add key map config screen
Add key mapping set dialog mockup
Fix static keyword hiding functions
Make KeyMap screen display current key mappings
Make keymap new key dialog display current key
Fix key map resolution only checking user settings

Alone the way a few other bugs got squashed
Merge branch 'master' of github.com:hrydgard/ppsspp
Fix a build error on linux platforms

Due to dl* function usage in Core/HW/atrac3plus.cpp on non-windows
platforms, Core library needs to be linked with -ldl flag on these
platforms.

Added a CoreExtraLibs variable in CMakeLists.txt to handle all
platform-dependent dependencies of Core, and added dl to this variable
on non-win32 platforms.
Use CMAKE_DL_LIBS instead of dl
Modified the dl link flag to linux platform only
Improve mpeg timestamp.

Read 6 bytes timestamp instead.
Merge pull request #2177 from oioitff/mpeg-fix

Improve mpeg timestamp.
Shortcut IdentifyFile (which is now used by GameInfoCache) by trusting the file extensions.