localrepo: use "vfs.rename()" instead of "util.rename()"
This patch makes "_journalfiles()" return a list of pairs of journal
file and corresponded vfs instance instead of a list of journal files
in full path, to use "vfs.rename()" instead of "util.rename()" in
"aftertrans()".
"undofiles()" still returns a list of undo files in full path, because
"repair.strip()" expects such list. It'll be also made to return a
list of pairs of undo file and corresponded vfs at vfs migration for
"repair.strip()" in the near future.