• overload for cos/sin/exp/atan2 to make cos(Math::BigInt->new(...)) work
  
• implemented blog() with a simple and fast "iterative" method
  
• use _log_int() in $CALC if possible
  
• cache $CALC->can(...) calls in global %CAN hash for speed
  
• reorder is_zero() check for band(), bior() and bxor() to speed up the
  case for when the underlying lib has _and(), _ior() and _xor()
  
• implement a new way of emulating AND, OR and XOR, this tremendously
  helps if band() et. al. are called with negative arguments
  
• try to call _signed_or(), _signed_and() and _signed_xor() in lib
  
• is_foobar() methods are slightly faster
  
• bnot() is about 12% faster
  
• bsqrt(): moved is_zero() || is_one() test out of the way => 28% faster
  for "small" values (Calc and GMP)
  
• small change for overload::constant
  
• bfac(): do 0 or 1 check only if CALC cannot do _fac() (thus faster)
  
• removed a needless _copy in bmod() with negative arguments (slightly faster)