Expose some activations

python/paddle/v2/fluid/layers/ops.py

 from ..registry import register_layer
-__all__ = [
-    'mean', 'mul', 'dropout', 'reshape', 'sigmoid', 'scale', 'transpose',
-    'sigmoid_cross_entropy_with_logits', 'elementwise_add', 'elementwise_div',
-    'elementwise_sub', 'elementwise_mul', 'clip', 'abs', 'sequence_softmax'
+
+__activations__ = [
+    'abs', 'tanh', 'sigmoid', 'relu', 'sqrt', 'ceil', 'floor', 'log', 'round'
 ]
 
+__all__ = [
+    'mean',
+    'mul',
+    'dropout',
+    'reshape',
+    'scale',
+    'transpose',
+    'sigmoid_cross_entropy_with_logits',
+    'elementwise_add',
+    'elementwise_div',
+    'elementwise_sub',
+    'elementwise_mul',
+    'clip',
+    'sequence_softmax',
+] + __activations__
+
 for _OP in set(__all__):
     globals()[_OP] = register_layer(_OP)