Mini proposal: rename float.min to float.min_normal

[Don]

This is another small imperfection we should get rid of.
The floating point types have a property called ".min", but unlike the 
integer ".min", it's not the minimum!
This naming stupidity is inherited from C++. The minimum float is 
-float.max. Instead, float.min is the minimum representable positive 
normalized number.
(BTW there are also representable "subnormal" numbers between 0 and 
float.min. So the name 'min' is _completely_ inappropriate, it's not 
even the minimum absolute value).

This misnaming is bad because (a) it causes confusion; and (b) it 
interfere with generic code, requiring special cases.
We should rename this while we have the chance. I don't think we should 
depart too far from the C/C++ name, but anything other than ".min" will 
work. I propose:

real.min ----> real.min_normal

Comments:
(1) Embedded underscores are probably not ideal, but they are already in 
use in the floating point properties mant_dig, and the rarely used 
max_10_exp, max_exp, min_10_exp, min_exp. They're also used in 
foreach_reverse, and in the built-in version identifiers, such as X86_64 
and D_InlineAsm_X86. So there seems no reason to avoid them here. But if 
you have a much better idea for a name, speak now!
(2) There's no need for float.max_normal. float.max truly is the maximum 
representable number (excluding infinity).
Although float.min sounds like some kind of inverse of float.max, it is 
not. (The relationship is: X.max * X.min = 4.0 for binary types, 10.0 
for decimal types).
Changing float.min -> float.min_normal will remove that illusion.

If there is no objection to this, I will create a patch. It's very simple.