Update files that depend on bbtsub functions to include bbtsub.h
Declare as static all functions in bbtsub.c that are not needed externally.
Add dependencies to makefile-tail.
new file: ../inc/bbtsub.h
modified: ../src/bbtsub.c
modified: ../src/colorbltfns.c
modified: ../src/draw.c
modified: ../src/misc7.c
modified: ../src/rawcolor.c
modified: ../src/subr.c
