As a prerequisite for cleaning up some other include issues, all the
include files in inc/ should have an include guard. All the xxxdefs.h
were created with them, but most older files were not.
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
