[SAGA-RG] just a couple of glitches in the Saga specs

[Ceriel Jacobs]

Hi Andre,

just a couple of minor glitches this time, and nothing debatable, I think.

The context class description still refers to the set_defaults method,
which no longer exists: "(see documentation to the set_defaults() method."
(at the bottom of page 81).

Notes at remove_context talk about "parameter values", that should be
"attribute values".

Cheers,		Ceriel