localrepo: use path expansion API via vfs
As a part of migration to vfs, this patch moves path expansion API
invocations in the constructor of "localrepository" to the constructor
of "opener", because the root path to the repository is very important
to handle paths using non-ASCII characters correctly.
This patch also rearrange initialization order of "wvfs" field,
because it is required to initialize "self.root".
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..