cmake compile under Mac OS X

1. Use `Accelerate / vecLib` as atlas by default if under OS X. Also the path for framework header files seem to changed a bit in OS X 10.10.
2. I moved the the library finding code from the `src/caffe` directory to top-level cmake script, too. Because I have problems finding header files when compiling for the `tools` directory.
3. A small fix to `gtest` is included by adding `-DGTEST_USE_OWN_TR1_TUPLE=1` to avoid compiling conflict (`fatal error: 'tr1/tuple' file not found`) with clang.