Fixing gflags HINTS variable names (adding missing “_DIR”).

- The HINTS variables for gflags were incorrectly used as
  GFLAGS_[INCLUDE/LIBRARY]_HINTS when they should have been
  GFLAGS_[INCLUDE/LIBRARY]_DIR_HINTS as per the docs.
- Also removing a completed TODO in the main CMakeLists.
- Updating method of extracting current directory in CeresConfig.cmake
  to avoid use of CMAKE_CURRENT_LIST_DIR, which was not present in
  CMake =< v2.8.3.

Change-Id: I42ae696e3b785febe48688d912f0f343e8947cb0
3 files changed