Update to version 8.4.18.  Distilled list of non-Windows changes:

	* generic/tclInterp.c (Tcl_GetAlias): fix for [Bug 1882373]

	* generic/regguts.h, generic/regc_color.c, generic/regc_nfa.c:
	Fixes for problems created when processing regular expressions that
	generate very large automata. An enormous number of thanks to Will
	Drewry <wad@google.com>, Tavis Ormandy <taviso@google.com>, and Tom
	Lane <tgl@sss.pgh.pa.us> from the Postgresql crowd for their help in
	tracking these problems down. [Bug 1810264]

	* unix/tclUnixCompat.c (TclpGetHostByName): Really applied
	the change noted on 2007-11-13 by dkf below.

	* generic/tclIOUtil.c (TclGetOpenMode): Only set the O_APPEND flag
	* tests/ioUtil.test (ioUtil-4.1):	on a channel for the 'a'
	mode and not for 'a+'. [Bug 1773127] (backport from HEAD)

	* generic/tclCmdIL.c (Tcl_LsearchObjCmd): Prevent shimmering crash
	when -exact and -integer/-real are mixed. [Bug 1844789]

	* generic/tclThread.c: Back-port locking changes from Tcl8.5
	in Tcl_Mutex/ConditionFinlize. Now we properly master-lock
	the finalization of sync primitives.

	* generic/regc_nfa.c:	Fixed infinite loop in the regexp compiler
	* generic/regcomp.c:	[Bug 1810038].  Corrected looping logic in
	* tests/regexp.test:	fixempties() to avoid wasting time walking a
	list of dead states [Bug 1832612].  Convert optst() from expensive
	no-op to a cheap no-op.  Improve newline usage in debug output.

	* unix/tclUnixCompat.c (TclpGetHostByName): The six-argument form of
	getaddressbyname_r() uses the fifth argument to indicate whether the
	lookup succeeded or not on at least one platform. [Bug 1618235]

	* generic/regc_lex.c (lexescape): Ensure that backreference numbers
	can't overflow a signed int in a way that breaks things. [Bug 1810264]

	* generic/tclParse.c (Tcl_ParseBraces): fix for possible read
	after the end of buffer, [Bug 1813528] (Joe Mistachkin).

	* generic/tclObj.c (Tcl_FindCommandFromObj): fix finding a deleted
	command; cannot trigger this from Tcl itself, but crash reported
	on xotcl. This check is new to 8.4 but exists in 8.5, so this is a
	backport or something. Thanks Gustaf Neumann.

	* generic/tcl.h (Tcl_DecrRefCount): Update change from 2006-05-29
	to make macro more warning-robust in unbraced if code.


(bjs)