* archive.c (bfd_ar_hdr_from_filesystem): support BFD_IN_MEMORY

	* archive.c (bfd_ar_hdr_from_filesystem): support BFD_IN_MEMORY
 	bfds; they have no "file" so we fake it.
	* bfd-in2.h: add bfd_make_writable and bfd_make_readable (regen)
	* libbfd.c (bfd_write): Allow writing to BFD_IN_MEMORY bfds by
 	resizing the memory buffer.
	* opncls.c (bfd_make_writable): New function; lets you write a
 	bfd_create'd bfd to an in-memory buffer.
	(bfd_make_readable): New function; lets you read back that buffer
 	as if it were from bfd_openr.  Used to build generated archive
 	members (winsup's ld's dlltool)