This whole thing was a false alarm.  Pilot error.
Read on if you are curious, but there should be
no 8.4 migration required for any ''internal'' hash
table, whatever that means.

Not entirely true, there are some very special cases 
(using specific internal Tcl structures in extensions), where
problems arise with cross-version compatibility.
See [Cross-version voodoo] for details. 
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[Michael A. Cleverly] reports on comp.lang.tcl:

 #if (TCL_MAJOR_VERSION == 8) && (TCL_MINOR_VERSION >= 4)
 #define Tcl_InitHashTableEx(x, y, z) Tcl_InitCustomHashTable(x, y, z)
 #endif

was needed to compile Ck.

MC (17 July): Actually in retrospect it was only needed because I was building with genkit (to build a tclkitck).  Ck itself has been updated by its maintainer for Tcl 8.4 at all yet, though it does compile and run fine.  ./configure must have found my 8.4a2 sources but the 8.4b1 header files (?). Sorry for any confusion. :-)
 
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So, apparently Ck was written to the interface
of Tcl 8.4a2?  It should be updated to use the interface
of Tcl 8.4b1.  As noted below, the name changed during
alpha development.

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From the  tcl ChangeLog:
  2001-01-18  Andreas Kupries  <a.kupries@westend.com>

	* Everything below belongs together, it fixes bug #123153.

	* generic/tcl.h (line 342): A bit more explanation about the
	  default value for TCL_PRESERVE_BINARY_COMPATABILITY.

	* generic/tcl.h (line 1208): Define the macro 'Tcl_InitHashTable'
	  only when TCL_PRESERVE_BINARY_COMPATIBILITY is not set
	  as it kills binary compatibility to 8.3 and earlier
	  versions. This is the main part of the patch/change.

	* generic/tcl.decls (line 1469):
	* generic/tclHash.c (Tcl_InitHashTable):
	* generic/tclHash.c (Tcl_InitHashTableEx):
	* generic/tclObj.c (Tcl_InitObjHashTable): Changed
	  'Tcl_InitHashTableEx' to 'Tcl_InitCustomHashTable'. This change
	  is more of an estethical nature, replacing the ubiquitous 'Ex'
	  suffix with a more meaningful name. The introduced binary
	  incompatibility is deemed acceptable as it is between alpha
	  versions.  Updated callers.

	* doc/Hash.3:
	* unix/mkLinks: Changed 'Tcl_InitHashTableEx' to
	  'Tcl_InitCustomHashTable'.

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%| [Changes in Tcl/Tk 8.4] | [Category Porting] |%
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