Log Message:
shells/{,static-,standalone}tcsh: Fix PKGREVISION & MAINTAINER.

The tcsh package Makefile is included directly by the static-tcsh
and standalone-tcsh Makefiles.  Modify some of the variables that
really need to be package-specific to be set with ?= in
tcsh/Makefile and document the package Makefiles that directly
include it.

Set PKGREVISION directly in static-tcsh and standalone-tcsh now
that they can have independent PKGREVISION values.

Bump the PKGREVISION of static-tcsh due to the MAINTAINER now
correctly being listed as agc@ due to this change.