Fixed CMake warnings

[mkoval]

This pull request sets the CMP0042 policy in CMake:

MACOSX_RPATH is enabled by default.

CMake 2.8.12 and newer has support for using @rpath in a target’s install name. This was enabled by setting the target property MACOSX_RPATH. The @rpath in an install name is a more flexible and powerful mechanism than @executable_path or @loader_path for locating shared libraries.

CMake 3.0 and later prefer this property to be ON by default. Projects wanting @rpath in a target’s install name may remove any setting of the INSTALL_NAME_DIR and CMAKE_INSTALL_NAME_DIR variables.

This policy was introduced in CMake version 3.0. CMake version 3.0.2 warns when the policy is not set and uses OLD behavior. Use the cmake_policy command to set it to OLD or NEW explicitly.

Setting this explicitly suppresses a warning when building with CMake >= 3.0 on OS X. From what I can tell online, @rpath is strictly better than the other options, so it is also a good thing to enable.

I also noticed that CMake was warning about an unused @only flag option in configure_file. It appears that this flag is case-sensitive, so I changed it to uppercase.

[jslee02]

It seems cmake less than 3.0.0 doesn't recognize this policy. There are some ways we can check if the policy is supported by the installed cmake. The second way looks good to me as:

if(POLICY CMP0042)
  # MACOSX_RPATH is enabled by default. This policy was introduced in CMake 3.0. 
  cmake_policy(SET CMP0042 NEW)
endif(POLICY CMP0042)

Travis-CI testing

[mkoval]

I added the if(POLICY CMP0042) check. Hopefully Travis will be happy now. 😓

[jslee02]

Looks good to me 👍 Waiting for Travis to be happy.