crypto tests: Wire into Makefiles

crypto tests: Wire into Makefiles

We make every .o file depend on $(cat_CATS) because that's easier than
trying to write out a list of which ones need the includes from
Catacomb.

(This is largely a commit by Mark Wooding supplied to me as a
work-in-progress, but I (Ian Jackson) have edited it to fit in with
the new subdirmk build system etc.)

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>