Convert to rich comparisons:

- sort's docompare() calls RichCompare(Py_LT).

- list_contains(), list_index(), listcount(), listremove() call
  RichCompare(Py_EQ).

- Get rid of list_compare(), in favor of new list_richcompare().  The
  latter does some nice shortcuts, like when == or != is requested, it
  first compares the lengths for trivial accept/reject.  Then it goes
  over the items until it finds an index where the items differe; then
  it does more shortcut magic to minimize the number of additional
  comparisons.

- Aligned the comments for large struct initializers.