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".
$ hg init
$ echo a > a
$ hg ci -qAm 'add a'
$ hg init subrepo
$ echo 'subrepo = http://example.net/libfoo' > .hgsub
$ hg ci -qAm 'added subrepo'
$ hg up -qC 0
$ echo ax > a
$ hg ci -m 'changed a'
created new head
$ hg up -qC 1
$ cd subrepo
$ echo b > b
$ hg add b
$ cd ..
Should fail, since there are added files to subrepo:
$ hg merge
abort: outstanding uncommitted changes in subrepository 'subrepo'
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