- removed debugging code in match()

- removed debugging code in match()
- added ex::match(const ex & pattern) which doesn't take a list as second
  argument
- expairseq::subs() substitutes in recombined pairs when the pattern is a
  product or a power; this is necessary for things like subs(2*x^2,x^2==3)
  because the first expression is mul(<x,2>,2) and only substituting in the
  "rest" part of the expair is not enough