statichttprepo.httprangeheader: implement readlines

bookmarks.readcurrent() requires readlines() on file objects returned from
repo.vfs. It isn't used right now but will be in upcoming patches.

mercurial/statichttprepo.py

@@ -54,8 +54,10 b' class httprangereader(object):'
             data = data[:bytes]
         self.pos += len(data)
         return data
+    def readlines(self):
+        return self.read().splitlines(True)
     def __iter__(self):
-        return iter(self.read().splitlines(True))
+        return iter(self.readlines())
     def close(self):
         pass