Merge remote-tracking branch 'qatar/release/0.5' into release/0.5

* qatar/release/0.5:
  update version
  Release notes and changelog for 0.5.5
  Fix ff_imdct_calc_sse() on gcc-4.6
  Make DECLARE_ALIGNED macros work with external array specifiers
  Fix MMX rgb24 to yuv conversion with gcc 4.6

Merged-by: Michael Niedermayer <michaelni@gmx.at>