Added check for CUDA toolkit version ( older can't compile Kepler )

cmake/OpenCVDetectCUDA.cmake

@@ -13,7 +13,7 @@ if(CUDA_FOUND)
 
   message(STATUS "CUDA detected: " ${CUDA_VERSION})
 
-  if("CUDA_VERSION_STRING" VERSION_GREATER "4.1")
+  if(${CUDA_VERSION_STRING} VERSION_GREATER "4.1")
     set(CUDA_ARCH_BIN "1.1 1.2 1.3 2.0 2.1(2.0) 3.0" CACHE STRING "Specify 'real' GPU architectures to build binaries for, BIN(PTX) format is supported")
   else()
     set(CUDA_ARCH_BIN "1.1 1.2 1.3 2.0 2.1(2.0)" CACHE STRING "Specify 'real' GPU architectures to build binaries for, BIN(PTX) format is supported")