Incompatible trig error handling

Two of the trigonometry functions have differing error condition behavior
between Linux and OSX. The Linux behavior follows the standard set by the
other trig functions.

On Linux:

SELECT asin(2);
> ERROR: input is out of range
>

SELECT acos(2);
> ERROR: input is out of range

On OSX:

SELECT asin(2);
> asin
> ------
> NaN
> (1 row)
>

SELECT asin(2);
> asin
> ------
> NaN
> (1 row)

The attached patch brings OSX into line with the expected behaviour and the
additional regression tests verify this.

Is this worth fixing and if so what is the next step?

Best, John