Missed ranged attacks go wildly astray

[mutability]

It seems that ranged attacks are either exactly on target (right tile) or wildly off target (miss by large angles), there is very little middle ground.

From a quick look, this is pretty suspicious (ranged.cpp, Creature::projectile_attack, in the "missed by at least one tile" path):

        // Cap spread at 30 degrees or it gets wild quickly
        double spread = std::min( dispersion / ARCMIN( 1 ), DEGREES( 30 ) );

This should be ARCMIN( dispersion ) not dispersion / ARCMIN( 1 ) if I'm reading the unit conversions right? dispersion is measured directly in arc-minutes AFAICS.

[mutability]

I think this originally got broken in c77a51f

[mutability]

Here's an example of firing around 100 arrows from a longbow (dispersion 210, precise shots) at a stationary turret - green = are the missed arrows.

210 arcminutes of dispersion should have them clustered within about 7 degrees (2 std dev), but clearly it's much more than that.

[mutability]

Same thing with the code changed as above: