atomictempfile: add read to the supported file operations

mercurial/util.py

@@ -1483,6 +1483,7 b' class atomictempfile(object):'
         self._checkambig = checkambig
 
         # delegated methods
+        self.read = self._fp.read
         self.write = self._fp.write
         self.seek = self._fp.seek
         self.tell = self._fp.tell

tests/test-atomictempfile.py

@@ -89,6 +89,13 b' class testatomictempfile(unittest.TestCa'
             # on other faster platforms can detect problems
             pass
 
+    def testread(self):
+        with open(self._filename, 'wb') as f:
+            f.write(b'foobar\n')
+        file = atomictempfile(self._filename, mode='rb')
+        self.assertTrue(file.read(), b'foobar\n')
+        file.discard()
+
 if __name__ == '__main__':
     import silenttestrunner
     silenttestrunner.main(__name__)