[Cook] Error in cook function documentation

[Florian Weimer]

The return value of the cook function is documented as:

 * RETURNS
 *	A word list containing true ("1") if all arguments are up-to-date,
 *	or false ("") if one or more could not.

Or, in the user guide:

.H 2 "cook"
This function requires one or more arguments,
filenames to be tested to see if they are up-to-date,
and be brought up-to-date if they are not.
The result are true ("1") if the files are (now) up-to-date,
or false ("") if they could not be built.

However, if I read the code correctly, the function returns a list of
file names which have been built successfully.