In util/ack, add prototypes and static to functions.

In util/ack, add prototypes and static to functions.

Declare most functions before using them.  I declare some functions in
ack.h and some in trans.h (because trans.h declares type trf).  I
leave declarations of scanb() and scanvars() in .c files because they
need type growstring.  (I can't #include "grows.h" in another header
file as long as grows.h doesn't guard against multiple inclusion.)

Functions used within one file become static.  I remove a few tiny
functions.  I move a few functions or declarations to more convenient
places.  Some functions now return void instead of a garbage int.

I feel that keyword "register" is obsolete, so I removed it from where
I was editing.  This commit doesn't touch mktables.c