pjsip: fix crash when using certain versions of libav

Ignore-this: 26fedc098fa58ef6ad81b5d3242f8a92

We are currently using avcodec_get_frame_default for initializing AVFrame
structures. Yes, it's a deprecated structure, but that's another story. We
happen to allocate those frames on the stack. FFMpeg and libav diverge in
what they do internally, as libav might allocate some buffer which needs
to be freed when setting the defaults. The crash was caused because libav
does a pointer comparison, but because we allocate the frame on the stack
but don't zero out the memory, pointers contained garbage.

TLDR: unitialized memory access / freeing because ffmpeg and libav differ
internally, yay!

darcs-hash:20141119170621-56b4d-fa8584764eeada95113b70acb389d51e04197dbb
Add build dependency on pkg-config

Ignore-this: 2dd12d46971bd6c719d8ca2806ba3b17

darcs-hash:20141120165256-56b4d-ffbf618c1c22d3d3b62f4e0489d3a0aa6cff8989
Add dependencies for video libraries

Ignore-this: 3bf7f9c4c7a3c090c513277d2faa60f9

darcs-hash:20141120170652-56b4d-12290261fff282ae9be1ee65dbe548f1b18f434d
Raised version and updated changelog

Ignore-this: c1fbb0e5e79a7072847a75a90921081c

darcs-hash:20141120173049-56b4d-1f29dcfae968106bb27a32765e2bad1d005892bf