Include more headers to declare functions.

Include more headers to declare functions.

This causes clang to give fewer warnings of implicit declarations of
functions.

In mach/pdp/cv/cv.c, rename wr_int2() to cv_int2() because it
conflicts with wr_int2() in <object.h>.

In util/ack, rename F_OK to F_TRANSFORM because it conflicts with F_OK
for access() in <unistd.h>.