- (l)degree(s), coeff(s, n) and collect(s) were extended to accept expressions

- (l)degree(s), coeff(s, n) and collect(s) were extended to accept expressions
  of any class (except add/mul/ncmul/numeric) for "s". They should even work
  if "s" is a "power" object, as long as the exponent is non-integer, but with
  some limitations. For example, you can "collect(a*2^x+b*2^x, 2^x)" to get
  "(a+b)*2^x", but "degree(2^(3*x), 2^x)" yields 0 instead of 3).