ensure global_step var is created in reuse=False

tensorpack/tfutils/common.py

@@ -45,6 +45,7 @@ def get_global_step_var():
         scope = tf.get_variable_scope()
         assert scope.name == '', \
                 "Creating global_step_var under a variable scope would cause problems!"
+        with tf.variable_scope(scope, reuse=False):
             var = tf.get_variable(GLOBAL_STEP_OP_NAME, shape=[],
                     initializer=tf.zeros_initializer,
                     trainable=False, dtype=tf.int32)