Files that #include "equiv.h" must do so after including "data.h", now
that a function prototype in equiv.h uses type rl_p from data.h.
Adjust style, changing some `for(...)` to `for (...)`. The style in
mach/proto/ncg is less than consistent; the big annoyance now is that
some files want tabs at 4 spaces, others want tabs at 8 spaces.
Put the declarations in "data.h", because that header declares the
types cost_t and token_p. Also #include <cgg_cg.h> from "data.h" to
get types c3_p and set_p, and guard <cgg_cg.h> against multiple
inclusion.
