- libavcodec issue
- some decoders alter AVCodecContext width/height values, in a wrong way
- eg. in issue 2815, vp6f decoder changes these values, resulting in distorted / invalid frames
- this patch forces default AVCodecContext values

Manager verison incremented;
Additional constatnt for library intialization added;
Documents updated.

cmpEps replaced on cmpEps2 to reduce code dublication;
Constants for cmpEps return values added.

range in calcHist() changed from [0,255] to [0,256]. Otherwise, it won't count pixels with value 255. It can be verified taking sum of histogram values and checking it with image size.