We just check equality of doubles using their bits, but +/- 0 have different bit representations and should compare equal.

case coid:
if( ((unsigned) l) != ((unsigned) r) )
return false;
l += 4; r += 4;
case cdate:
case cdouble:
if( *((unsigned long long *) l) != *((unsigned long long *) r) )
return false;
l += 8; r += 8;
break;

I wrote a test, will push it once buildbot is working.