Static initialization should use static initializer

[zeen]

Given code like

static var x = 5;

we get code like this:

static int x;
+ (int) x {
    if (x == nil) x = 50;
    return x;
}

This breaks badly for non-Dynamic types. Even for Dynamic types, it becomes impossible to set such a variable to null later on in the code, because on next access, it's reinitialized again. So these assignments should be done in a static initializer (#7).

Also, lack on an initialization value leads to bad code:

static var x;

leads to:

static int x;
+ (int) x {
    if (x == nil) x = ; // <-- invalid code
    return x;
}