function kernelBetainc( x, a, b, regularized, upper ) {
	return compute( x, a, b, regularized, upper, [ 0.0, 0.0 ], 1, 0 );
}
Evaluates the incomplete beta function and its first derivative.

@param {Probability} x - function input
@param {NonNegativeNumber} a - function parameter
@param {NonNegativeNumber} b - function parameter
@param {boolean} regularized - boolean indicating if the function should evaluate the regularized boolean beta function
@param {boolean} upper - boolean indicating if the function should return the upper tail of the incomplete beta function instead
@returns {Array} function value and first derivative

@example
var out = kernelBetainc( 0.5, 2.0, 2.0, false, false );
// returns [ ~0.083, ~1.5 ]

@example
var out = kernelBetainc( 0.2, 1.0, 2.0, true, false );
// returns [ 0.36, 1.6 ]