Remove the distinction between inline/outline storage for bytevectors.

Remove the distinction between inline/outline storage for bytevectors.

* libguile/bytevectors.c (SCM_BYTEVECTOR_INLINE_THRESHOLD,
  SCM_BYTEVECTOR_INLINEABLE_SIZE_P, SCM_BYTEVECTOR_SET_CONTENTS,
  SCM_BYTEVECTOR_SET_INLINE): Remove.
  (SCM_BYTEVECTOR_HEADER_BYTES): New macro.
  (SCM_BYTEVECTOR_SET_ELEMENT_TYPE): Adjust to new flag layout.
  (make_bytevector): Remove content inlining machinery; use
  `scm_gc_malloc_pointerless ()' in all cases; special-case zero-sized
  vu8 buffers.
  (make_bytevector_from_buffer): Simplified.
  (scm_c_shrink_bytevector): New, formerly `scm_i_shrink_bytevector ()'.
  Remove buffer inlining machinery.
  (scm_bootstrap_bytevectors): Use `make_bytevector ()' for
  SCM_NULL_BYTEVECTOR.

* libguile/bytevectors.h (SCM_BYTEVECTOR_HEADER_SIZE): New macro.
  (SCM_BYTEVECTOR_CONTENTS): Adjust to new layout.
  (SCM_SET_BYTEVECTOR_FLAGS): Properly cast F.
  (SCM_F_BYTEVECTOR_INLINE, SCM_BYTEVECTOR_INLINE_P): Remove.
  (SCM_BYTEVECTOR_ELEMENT_TYPE): Adjust.
  (scm_c_shrink_bytevector): Remove macro, make a C function
  declaration.