[PATCH] Clarify issues with SPI and C language function limitations

[Please CC any replies]

Hi,

Here is a patch to the documentation clarifying some minor issues.

The first is to the main SPI documentation clarifying that SPI isn't
available unless there is a current snapshot (leading to the "no
snapshot has been set" error).

The second clarifies when the get_fn_expr_rettype() and
get_fn_expr_argtype() functions can actually provide the information
requested.

Have a nice day,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.