Eliminate the baroque floating-point operators a la !<>=

[Don]

Andrei Alexandrescu wrote:
> Don wrote:
>> Inclusion of the NCEG operators was a bit of tokenism, making a _very_ 
>> strong statement that D took numerical programmers seriously. But I 
>> think D's at the point where it can make that statement without 
>> relying on tokenism.
> 
> So is it ok to yank them?
> 
> Andrei

Yes if and only if we get agreement from Tango that tango2.math can use 
std.math.

There's one other minor issue:
isNaN() isn't supposed to trigger on signalling NaNs, but !<>= should 
trigger them. I'm not sure that _anyone_ actually cares about this 
difference (you can use isSignallingNaN() in the rare case where you 
don't want to trigger it), but it would be a difference from IEEE if we 
signalled when isNaN() is called, which is what would happen if we 
recreated the !<>= operators by merging isNaN with <,>, =.