New compile-system procedure. Replaced ffi.sf and ffi.cbf.

New compile-system procedure.  Replaced ffi.sf and ffi.cbf.

* src/compiler/base/toplev.scm (compile-file): Only declare
integrate-external when dependencies have no type.  Thus a dependency
on e.g. "gtk-const.bin" might cause the dependent file to be
re-compiled without a spurious warning about a missing .ext file.

* src/cref/: butils.scm, cref.pkg: Added new file butils.scm,
containing a compile-system procedure that applies compile-file to
each file mentioned in a .pkg file.

* src/ffi/: compile.scm, ffi.cbf, ffi.sf: Replaced the old .cbf and
.sf files with a new, modern compile.scm file.