degree(), ldegree(), coeff(), lcoeff(), tcoeff() and collect() can now

degree(), ldegree(), coeff(), lcoeff(), tcoeff() and collect() can now
be used with constants and indexed expressions as well, so you can use
it to collect by powers of Pi or find the coefficient of gamma~0.
Limitations:
 - it only works with symbols, constants and indexed expressions;
   trying to find the coefficient of, e.g., "x^2" or "x+y" won't work
 - it does not know about dummy index summations; the coefficient of
   gamma~0 in p.mu*gamma~mu should be p.0 but is returned as 0
 - using the functions on elements of noncommutative products might
   return wrong or surprising results