gray decoding regression

[Carl Eugen Hoyos]

​http://thread.gmane.org/gmane.comp.video.ffmpeg.user/50518/focus=50526
H264 decoding with -flags +gray is broken for for P-frames and B-frames, regression since bb29ee62 / d2a25c40
out.avi is green except for input I-frames:

$ ffmpeg -flags +gray -i fate-suite/h264/extreme-plane-pred.h264 -qscale 2 out.avi
ffmpeg version N-60713-g1355caf Copyright (c) 2000-2014 the FFmpeg developers
  built on Feb 18 2014 16:50:43 with gcc 4.7 (SUSE Linux)
  configuration: --enable-gpl --enable-gray
  libavutil      52. 64.100 / 52. 64.100
  libavcodec     55. 52.102 / 55. 52.102
  libavformat    55. 33.100 / 55. 33.100
  libavdevice    55. 10.100 / 55. 10.100
  libavfilter     4.  1.102 /  4.  1.102
  libswscale      2.  5.101 /  2.  5.101
  libswresample   0. 17.104 /  0. 17.104
  libpostproc    52.  3.100 / 52.  3.100
Input #0, h264, from 'fate-suite/h264/extreme-plane-pred.h264':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: h264 (High), yuv420p, 352x288, 25 fps, 25 tbr, 1200k tbn, 50 tbc
Please use -q:a or -q:v, -qscale is ambiguous
Output #0, avi, to 'out.avi':
  Metadata:
    ISFT            : Lavf55.33.100
    Stream #0:0: Video: mpeg4 (FMP4 / 0x34504D46), yuv420p, 352x288, q=2-31, 200 kb/s, 25 tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (h264 -> mpeg4)
Press [q] to stop, [?] for help
frame=  100 fps=0.0 q=2.0 Lsize=    3532kB time=00:00:04.00 bitrate=7232.8kbits/s
video:3524kB audio:0kB subtitle:0 data:0 global headers:0kB muxing overhead 0.225428%

[Michael Niedermayer]

Fixed in 72e691314027b08955679319394dd0d8477973b7