Revert cmake modification in this pr.

CMakeLists.txt

@@ -12,12 +12,8 @@ include(package)
 find_package(SWIG 2.0)
 find_package(CUDA QUIET)
 find_package(Protobuf REQUIRED)
-
-# Set up the versions we know about, in the order we will search.
-# Always add the user supplied additional versions to the front.
-set(Python_ADDITIONAL_VERSIONS 2.7)
-find_package(PythonInterp 2.7 REQUIRED)
 find_package(PythonLibs 2.7 REQUIRED)
+find_package(PythonInterp 2.7 REQUIRED)
 find_package(ZLIB REQUIRED)
 find_package(NumPy REQUIRED)
 find_package(Threads REQUIRED)