[Rd] dgamma error condition?

[Ben Bolker]

   There's an apparent inconsistency between the
behavior of d(pqr)gamma and other distribution
functions for "bad" parameter values.  Specifically,
most distributions give NaN and a warning for bad
parameters (e.g. probabilities <0 or >1).  In contrast,
d(pqr)gamma actually gives an error and stops when shape<0.
I don't see why it has to be this way -- the internal
C code is set up to detect shape<0 (or scale<0) and
return NaN and a warning, and none of the other
distribution functions in that bit of the code have
similar behavior.

   It would seem more consistent (and would be more
convenient for me -- the error-instead-of-warning
is making me have to jump through additional hoops)
if dgamma just returned NaN and a warning.

    Any thoughts?

   cheers
     Ben Bolker