Warn when trying to dither to 1 bit
Warn when trying to dither to 1 bit

Dithering to 1 bit resolution doesn't work with the general-purpose
routines since, for signed integer, only the sign bit is available
at 1 bit. The dither effect will clip on each sample. So, for now,
issue a warning and give up.

mhartzel/sox_personal_fork,CaptainHayashi/sox,CaptainHayashi/sox,uklauer/sox,MageSlayer/sox,CaptainHayashi/sox,pcqpcq/sox,Distrotech/sox,davel/sox,Motiejus/sox,cbagwell/sox,jacksonh/sox,MageSlayer/sox,pcqpcq/sox,jacksonh/sox,Motiejus/sox,MageSlayer/sox,Motiejus/sox,cbagwell/sox,Distrotech/sox,mhartzel/sox_personal_fork,uklauer/sox,Motiejus/sox,mhartzel/sox_personal_fork,pcqpcq/sox,MageSlayer/sox,davel/sox,jacksonh/sox,jacksonh/sox,cbagwell/sox,MageSlayer/sox,Distrotech/sox,Distrotech/sox,davel/sox,CaptainHayashi/sox,uklauer/sox,davel/sox,mhartzel/sox_personal_fork,uklauer/sox,cbagwell/sox,pcqpcq/sox