Use "pointer" instead of "foreign" when dealing with wrapped pointers.

Use "pointer" instead of "foreign" when dealing with wrapped pointers.

* libguile/foreign.h (scm_t_foreign_finalizer): Rename to...
  (scm_t_pointer_finalizer): ... this.
  (SCM_FOREIGN_P): Rename to...
  (SCM_POINTER_P): this.
  (SCM_VALIDATE_FOREIGN): Rename to...
  (SCM_VALIDATE_POINTER): ... this.
  (SCM_FOREIGN_HAS_FINALIZER): Rename to...
  (SCM_POINTER_HAS_FINALIZER): ... this.
  (scm_take_foreign_pointer): Rename to...
  (scm_from_pointer): ... this.
  (scm_foreign_address): Rename to...
  (scm_pointer_address): ... this.
  (scm_foreign_to_bytevector): Rename to...
  (scm_pointer_to_bytevector): ... this.
  (scm_foreign_set_finalizer_x): Rename to...
  (scm_set_pointer_finalizer_x): ... this.
  (scm_bytevector_to_foreign): Rename to...
  (scm_bytevector_to_pointer): ... this.
  (scm_i_foreign_print): Rename to...
  (scm_i_pointer_print): ... this.

* libguile/foreign.c: Update accordingly.

* libguile/tags.h (scm_tc7_foreign): Rename to...
  (scm_tc7_pointer): ... this.

* libguile/foreign.c, libguile/deprecated.c, libguile/dynl.c,
  libguile/evalext.c, libguile/gc.c, libguile/goops.c, libguile/gsubr.c,
  libguile/gsubr.h, libguile/print.c, libguile/snarf.h,
  libguile/vm-i-system.c, module/system/foreign.scm,
  test-suite/standalone/test-ffi, test-suite/tests/foreign.test: Update
  accordingly.