function hyp2f1( a, b, c, x ) {
	return addon( a, b, c, x );
}
Evaluates the Gaussian hypergeometric function.

@private
@param {number} a - input value
@param {number} b - input value
@param {number} c - input value
@param {number} x - input value
@returns {number} function value

@example
var v = hyp2f1( 1.0, 1.0, 1.0, 0.0 );
// returns 1.0

@example
var v = hyp2f1( 10.0, 7.4, -1.8, -0.99 );
// returns ~0.423

@example
var v = hyp2f1( 10.0, 1.0, -1.8, -0.99 );
// returns ~-0.875

@example
var v = hyp2f1( 2.0, 3.0, 5.0, 0.99 );
// returns ~27.699

@example
var v = hyp2f1( 3.0, 4.0, 7.0, 1.0 );
// returns +Infinity

@example
var v = hyp2f1( NaN, 3.0, 2.0, 0.5 );
// returns NaN

@example
var v = hyp2f1( 1.0, NaN, 2.0, 0.5 );
// returns NaN