localrepo: use vfs instead of "os.path.*" in sharedpath checking

In the point of view of efficiency, "vfs" instance created in this
patch should be passed to and reuse in "store.store()" invocation just
after patched code block, because "store" object is initialized by vfs
created with "self.sharedpath".

eBut to focus just on migration from direct file I/O API accessing to
vfs, this patch uses created vfs as temporary one. Refactoring around
"store.store()" invocation will be done in the future.

mercurial/localrepo.py

@@ -209,8 +209,10 b' class localrepository(object):'
 
         self.sharedpath = self.path
         try:
-            s = os.path.realpath(self.opener.read("sharedpath").rstrip('\n'))
-            if not os.path.exists(s):
+            vfs = scmutil.vfs(self.vfs.read("sharedpath").rstrip('\n'),
+                              realpath=True)
+            s = vfs.base
+            if not vfs.exists():
                 raise error.RepoError(
                     _('.hg/sharedpath points to nonexistent directory %s') % s)
             self.sharedpath = s