Include stat-macros.h, xalloc.h.

Include stat-macros.h, xalloc.h.
(S_ISDIR, S_ISUID, S_ISGID, S_ISVTX, S_IRUSR, S_IWUSR, S_IXUSR):
(S_IRGRP, S_IWGRP, S_IXGRP, S_IROTH, S_IWOTH, S_IXOTH, S_IRXWU):
(S_IRWXG, S_IRWXO, CHMOD_MODE_BITS):
Remove.  This is now stat-macros.h's job.
(talloc): Remove.  All callers replaced by xalloc, so that
our invokers don't have to worry about reporting memory failures.
(make_node_op_equals): Remove.
(MODE_ORDINARY_CHAGE, MODE_X_IF_ANY_X, MODE_COPY_EXISTING):
New constants.
(struct mode_change): Moved here from modechange.h.
(mode_append_entry): Remove.
(mode_compile): Remove MASKED_OPS arg, since it encouraged
apps to have incorrect behavior.  Use simpler algorithm for head
and tail.  Don't futz with umask; that's now the job of mode_adjust.
Detect more invalid usages rather than having somewhat-random behavior.
Don't insert an "a=" action, as that leads to incorrect behavior.
(mode_compile, mode_create_from_ref): Return NULL on error instead
of an enum, since now there's only one way to have an error.  All
callers changed.
(mode_adjust): Accept new arg UMASK_VALUE, and interpret it
at the correct time.  Simplify calculation of "+u" and its ilk.
Don't mishandle "+X".
(mode_free): Remove "register" and localize decls.