We check the required Tcl version number before we setup msgcat for
language translation. If the Tcl version is too old just display the
untranslated error text.
The caller of show_error can now pass an alternative function for mc.
The Tcl list function turns the translation into a no-op.
This fixes the error:
Error in startup script: invalid command name "mc"
when attempting to start gitk with Tcl 8.3.
Tested with both Tcl 8.3 and 8.4.
Signed-off-by: Bernt Hansen <bernt@norang.ca> Signed-off-by: Paul Mackerras <paulus@samba.org>