#4848 No way to directly evaluate beta(-1.5, 0.5), while beta(-3/2, 1/2) becomes zero

[David Scherfgen]

(%i1) beta(-3/2, 1/2);
(%o1) 0

(%i2) beta(-1.5, 0.5);
(%o2) beta(-1.5, 0.5)

(%i3) beta(-1.5b0, 5.0b-1);
(%o3) beta(-1.5b0, 5.0b-1)