List problematic files when building

[KwadroNaut]

Some, but not all problematic files are being printed during building.

Processing files  [###################################-]  102133/104246  0d 00:01:23/usr/local/lib/python2.7/dist-packages/PIL/Image.py:2438: DecompressionBombWarning: Image size (125632512 pi
xels) exceeds limit of 89478485 pixels, could be decompression bomb DOS attack.      
  DecompressionBombWarning)                                                          
Processing files  [####################################]  104246/104246              
ERROR: Some files have failed to be processed:                                       
ERROR:   - 2008/09/08/mvi_2540.webm                                                  

I think that such files should also be listed during build, without debug verbose options. Failure on the videos could be accompanied with some hint like 'did you install ffmpeg?'

[saimn]

Right, this could be improved.