basefilectx: move p1 from filectx

mercurial/context.py

@@ -550,6 +550,9 b' class basefilectx(object):'
         return [filectx(self._repo, p, fileid=n, filelog=l)
                 for p, n, l in pl if n != nullid]
 
+    def p1(self):
+        return self.parents()[0]
+
 class filectx(basefilectx):
     """A filecontext object makes access to data related to a particular
        filerevision convenient."""
@@ -635,9 +638,6 b' class filectx(basefilectx):'
                 pass
         return renamed
 
-    def p1(self):
-        return self.parents()[0]
-
     def p2(self):
         p = self.parents()
         if len(p) == 2: