As of now, it is not possible to find OpenSceneGraph in Debug because the only
variable find_package_handle_standard_args is checking is ${module}_LIBRARY
while the debug library is in ${module}_LIBRARY_DEBUG. The refactoring gets rid
of the old behaviour to replace with a call to select_library_configurations
which will populated ${module}_LIBRARY accordingly.

[Modules/Findosg_functions.cmake Modules/FindOpenThreads.cmake]
- Include SelectLibraryConfigurations module
- Modify the name of the variable that will be populated by the first
  find_library to ${MODULE}_LIBRARY_RELEASE so that SelectLibraryConfigurations
can act on it
- Add call to select_library_configurations after attempting to find libraries
  in debug and release