* init.scm (index, rindex): replace versions in utilities.scm with

	* init.scm (index, rindex): replace versions in utilities.scm with
	primitives.
	load errno.scm.

	* netconst.scm: undefine maybe-define and maybe-define-so after use.
	* errno.scm: new file.

	* fports.c (scm_open_file): pass errno to scm_syserror_msg.
	* filesys.h: update prototypes.  Remove macros: SCM_FD_P, SCM_FD_FLAGS,
	SCM_FD.
	* filesys.c (scm_sys_stat, scm_sys_lstat): pass errno to
	scm_syserror_msg.
*	(scm_sys_read_fd, scm_sys_write_fd, scm_sys_close, scm_sys_lseek,
	scm_sys_dup): deleted: FD capability will be added to other
	procedures.
*	Remove support for the FD object type: scm_tc16_fd, scm_fd_print,
	scm_fd_free, fd_smob, scm_intern_fd.
*	(scm_open): renamed from scm_sys_open.  Return a port instead of
	an FD object.  Make the mode argument optional.
*	(scm_sys_create): deleted, it's just a special case of open.
	(scm_init_filesys): move interning of constants O_CREAT etc.,
	here (were previously using SCM_CONST_LONG macro).
	Add missing constants: O_RDONLY, O_WRONLY, O_RDWR, O_CREAT.
	don't newsmob fd.
	(numerous _sys_ procedures): remove gratuitous _sys_ from names.
	include "fports.h" and <stdio.h>
	(scm_stat, scm_select): don't support FD objects.

	* error.h: adjust scm_syserror_msg prototype.
	* error.c (scm_syserror_msg): take an extra argument for errno.
	Using the global value didn't always work, since it could be
	reset by procedure calls in the message or args arguments.

	* fports.c (scm_setbuf0): call setbuf even if FIONREAD is not defined.
	I don't understand why the check was there (and what about the
	ultrix check?)

	* strop.c (scm_string_copy): allow shared substrings to be copied.

	* unif.h: corresponding change to prototypes.
	* unif.c (scm_uniform_array_read_x, scm_uniform_array_write_x):
	recognize two new optional arguments: offset and length.  Allow
	the port argument to be an integer (file descriptor, for scsh).
	Include <unistd.h> for "read" prototype.