Revert "Converted relative imports to absolute."

theano/tensor/nnet/__init__.py

-from theano.tensor.nnet import *
-from theano.tensor.nnet.conv import conv2d, ConvOp
-from theano.tensor.nnet.Conv3D import *
-from theano.tensor.nnet.ConvGrad3D import *
-from theano.tensor.nnet.ConvTransp3D import *
-from theano.tensor.nnet.sigm import softplus, sigmoid, sigmoid_inplace, scalar_sigmoid
+from nnet import *
+from conv import conv2d, ConvOp
+from Conv3D import *
+from ConvGrad3D import *
+from ConvTransp3D import *
+from sigm import softplus, sigmoid, sigmoid_inplace, scalar_sigmoid