unionrevlog: extract 'baserevision' and 'baserevdiff' methods
This makes possible to use unionrevlog class with subclasses of revlog that
override revlog's 'revision' and 'revdiff' methods. In particular this change
is necessary to implement manifest compression, as it allows extension to
replace manifest class and override 'revision' amd 'revdiff' methods there.
$ for i in aaa zzz; do
> hg init t
> cd t
>
> echo
> echo "-- With $i"
>
> touch file
> hg add file
> hg ci -m "Add"
>
> hg cp file $i
> hg ci -m "a -> $i"
>
> hg cp $i other-file
> echo "different" >> $i
> hg ci -m "$i -> other-file"
>
> hg cp other-file somename
>
> echo "Status":
> hg st -C
> echo
> echo "Diff:"
> hg diff -g
>
> cd ..
> rm -rf t
> done
-- With aaa
Status:
A somename
other-file
Diff:
diff --git a/other-file b/somename
copy from other-file
copy to somename
-- With zzz
Status:
A somename
other-file
Diff:
diff --git a/other-file b/somename
copy from other-file
copy to somename