obsstore: initialize _all markers without using _addmarkers()

The next patch will make _all variable propertycached to avoid costly parsing
of obsstore. This means we can't call _addmarkers() to initialize _all.

Because all cached markers depend on _all, it isn't necessary to update these
caches when _all is initially loaded.

mercurial/obsolete.py

@@ -527,7 +527,9 b' class obsstore(object):'
         self._readonly = readonly
         if data:
             self._version, markers = _readmarkers(data)
-            self._addmarkers(markers)
+            markers = list(markers)
+            _checkinvalidmarkers(markers)
+            self._all = markers
 
     def __iter__(self):
         return iter(self._all)