Improve agfiles rule. (1) It didn't depend on $(AGCL) and it absolutely should have. (2) allow AGFORCE=1 to make it rebuild whether or not it looks out of date. (3) Document this.

#!/bin/sh
# cppfilt - wrap the IBM compiler's cppfilt
# (all this does is run wine)

WINEPATH='I:\\ibmcppw\\bin'
export WINEPATH

exec wine 'I:\\ibmcppw\\bin\cppfilt.exe' "$@"