Add protos for positive keywords

Add protos for positive keywords

‘Positive’ means having a + before it in regen/keywords.pl; i.e., key-
words that cannot be overridden.

Since all keywords are going to be added as subs to the CORE:: name-
space, with prototypes wherever they can apply, it makes sense to
return prototypes for all that can have them, which turns out to be
only a handful.