pb: Allow for nested messages pretty specification
pb: Allow for nested messages pretty specification

It's not perfect, only the depth is taken into account,
not the field number, but this is OK for now.

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

biddyweb/criu,tych0/criu,gonkulator/criu,KKoukiou/criu-remote,gablg1/criu,wtf42/criu,svloyso/criu,marcosnils/criu,tych0/criu,gablg1/criu,kawamuray/criu,AuthenticEshkinKot/criu,gonkulator/criu,LK4D4/criu,gablg1/criu,sdgdsffdsfff/criu,LK4D4/criu,efiop/criu,wtf42/criu,biddyweb/criu,ldu4/criu,ldu4/criu,eabatalov/criu,svloyso/criu,fbocharov/criu,fbocharov/criu,eabatalov/criu,ldu4/criu,fbocharov/criu,sdgdsffdsfff/criu,LK4D4/criu,KKoukiou/criu-remote,biddyweb/criu,kawamuray/criu,AuthenticEshkinKot/criu,KKoukiou/criu-remote,svloyso/criu,biddyweb/criu,gablg1/criu,biddyweb/criu,efiop/criu,gonkulator/criu,wtf42/criu,ldu4/criu,kawamuray/criu,kawamuray/criu,AuthenticEshkinKot/criu,svloyso/criu,marcosnils/criu,svloyso/criu,eabatalov/criu,fbocharov/criu,marcosnils/criu,efiop/criu,wtf42/criu,marcosnils/criu,eabatalov/criu,eabatalov/criu,tych0/criu,marcosnils/criu,rentzsch/criu,rentzsch/criu,KKoukiou/criu-remote,efiop/criu,rentzsch/criu,kawamuray/criu,eabatalov/criu,gonkulator/criu,sdgdsffdsfff/criu,LK4D4/criu,fbocharov/criu,LK4D4/criu,svloyso/criu,gonkulator/criu,wtf42/criu,rentzsch/criu,ldu4/criu,gablg1/criu,ldu4/criu,AuthenticEshkinKot/criu,gonkulator/criu,sdgdsffdsfff/criu,LK4D4/criu,sdgdsffdsfff/criu,tych0/criu,kawamuray/criu,efiop/criu,tych0/criu,rentzsch/criu,tych0/criu,rentzsch/criu,gablg1/criu,fbocharov/criu,KKoukiou/criu-remote,marcosnils/criu,KKoukiou/criu-remote,wtf42/criu,sdgdsffdsfff/criu,AuthenticEshkinKot/criu,efiop/criu,biddyweb/criu,AuthenticEshkinKot/criu