Compare helper functions for writing opCmps

[Bill Baxter]

Often an opCmp implementation will end up just being a comparison based 
on a single member of elementary type.

Is there any function in Phobos for doing an opCmp style comparison of 
the basic types?  Something like

int compare(S,T)(S a, T b) {
     if (a==b) return 0;
     return (a<b)? -1 : 1;
}

It's simple but comes up enough that it seems like it would be useful to 
have in the library.  Kinda like min/max.... which aren't in Phobos either.

-bb