Made CMake's search for cuDNN a little more broad

dlib/dnn/test_for_cudnn/find_cudnn.txt

@@ -3,15 +3,14 @@ message(STATUS "Looking for cuDNN install...")
 # Look for cudnn, we will look in the same place as other CUDA
 # libraries and also a few other places as well.
 find_path(cudnn_include cudnn.h
-    HINTS ${CUDA_INCLUDE_DIRS} $ENV{CUDNN_INCLUDE_DIR} 
-    PATHS /usr/local/include
+    HINTS ${CUDA_INCLUDE_DIRS} ENV CUDNN_INCLUDE_DIR  ENV CUDNN_HOME
+    PATHS /usr/local ENV CPATH
+    PATH_SUFFIXES include
     )
 get_filename_component(cudnn_hint_path ${CUDA_CUBLAS_LIBRARIES} PATH)
 find_library(cudnn cudnn
-    HINTS ${cudnn_hint_path} $ENV{CUDNN_LIBRARY_DIR}
-    PATHS /usr/local/lib64 
-            /usr/local/cuda/lib64
-            /usr/local/cuda/lib
-            /usr/local/lib
+    HINTS ${cudnn_hint_path} ENV CUDNN_LIBRARY_DIR  ENV CUDNN_HOME 
+    PATHS /usr/local /usr/local/cuda ENV LD_LIBRARY_PATH
+    PATH_SUFFIXES lib64 lib
     )
 mark_as_advanced(cudnn cudnn_include)