Add option to dump frame-averaged PSNR to dump_psnr.c.
Add option to dump frame-averaged PSNR to dump_psnr.c.

xiph/daala,xiphmont/daala,xiph/daala,HeadhunterXamd/daala,luctrudeau/daala,xiph/daala,HeadhunterXamd/daala,ycho/daala,xiph/daala,ycho/daala,luctrudeau/daala,HeadhunterXamd/daala,ycho/daala,xiphmont/daala,HeadhunterXamd/daala,luctrudeau/daala,ycho/daala,xiphmont/daala,xiph/daala,xiphmont/daala,ycho/daala,xiphmont/daala,luctrudeau/daala,luctrudeau/daala,HeadhunterXamd/daala