bug#6980: Could goto-char please have its own history list?

[Juri Linkov]

> I can't see no reason its history should be mixed by something else.
> (More than devel historic reasons ;-)

It makes sense to share the same history that contains only numeric
values between all commands that use `read-number', like
e.g. `goto-line' and `goto-char' (with some changes), because
non-numeric values (added to the history from other commands)
are useless for such number-reading commands.