scmutil: turn opener._audit into a property, mustaudit

This will be used by an upcoming patch.

mercurial/scmutil.py

@@ -229,13 +229,21 b' class opener(abstractopener):'
         if expand:
             base = os.path.realpath(util.expandpath(base))
         self.base = base
-        self._audit = audit
-        if audit:
-            self.auditor = pathauditor(base)
+        self._setmustaudit(audit)
+        self.createmode = None
+        self._trustnlink = None
+
+    def _getmustaudit(self):
+        return self._audit
+
+    def _setmustaudit(self, onoff):
+        self._audit = onoff
+        if onoff:
+            self.auditor = pathauditor(self.base)
         else:
             self.auditor = util.always
-        self.createmode = None
-        self._trustnlink = None
+
+    mustaudit = property(_getmustaudit, _setmustaudit)
 
     @util.propertycache
     def _cansymlink(self):