[Maxima] gamma_incomplete(1/2,0)?

[Raymond Toy]

Current CVS says gamma_incomplete(1/2,0) is sqrt(%pi)/2.  But the help
for gamma_incomplete says gamma_incomplete(a,z) =
integrate(exp(-t)*t^(a-1),t,0,z).  (This matches A&S 6.5.2.)

So from the documentation, I would expect the integral to be 0.

Which is correct?  Since A&S is our reference, I think the current value
is incorrect and we should return 0.

Ray