Created by: luotao1

when running gpu demo, if users don't have the correct cudnn pass:

I0512 16:12:11.301077 22465 Util.cpp:166] commandline:  --use_gpu=True --trainer_count=1 
F0512 16:12:11.792135 22465 DynamicLoader.cpp:104] Check failed: nullptr != *dso_handle Failed to find dynamic library: libcudnn.so (libcudnn.so: cannot open shared object file: No such file or directory) 
Please specify its path correctly using one of the following ways: 
Method 1. set cuda and cudnn lib path at runtime. http://www.paddlepaddle.org/doc/ui/cmd_argument/argument_outline.html 
For instance, issue command: paddle train --use_gpu=1 --cuda_dir=/usr/local/cuda/lib64 --cudnn_dir=/usr/local/cudnn/lib ...
Method 2. set environment variable LD_LIBRARY_PATH on Linux or DYLD_LIBRARY_PATH on Mac OS. 
For instance, issue command: export LD_LIBRARY_PATH=... 

The url in Method 1 can not open now.