* Makefile.in (VERSION): Roll to 4.6.8.

* Makefile.in (VERSION):  Roll to 4.6.8.
(OBS):  Put version.o first, so Makefile rebuild happens early.

* command.h:  Publicize prototype for not_just_help_class_command.
* command.c:  Remove proto.
* maint.c:  Mark "mt" as an abbrev, to avoid duplicated help
output.  Move "maint info" from class info to class maintenance,
and improve text.
* infrun.c:  Move "stop" to class_obscure, and give it a
function so it will not be seen as a global help topic.  FIXME,
it should be possible to set these attributes independently.

* core.c (core_command):  Make nicer error message for no core support.