Update .gitignore
FindPkgConfig: Fix file([TO_CMAKE_PATH|TO_NATIVE_PATH]) for PKG_CONFIG_PATH unset
FindDRAGONFLYAPI: Cleanup
FindOpenCV: Cleanup

Do not mark OpenCV_DIR as advanced
MacroUninstallTarget: Do not fail with FATAL_ERROR if install_manifest.txt is missing
Set version correctly in YCMConfig.cmake
FindOrBuildPackage: Add missing copyright statement
Add include guards
Use "${ARGN}" instead of ${ARGN} with cmake_parse_arguments
Download CMake files from CMake git instead of including them.

Delete no longer needed files.

Split installed files in
- cmake-2.8.8 (used only if cmake <= v2.8.7)
- cmake-2.8.12 (used only if cmake <= 2.8.11.2)
- cmake-next (patches merged but not yet released)
- cmake-proposed (patches not merged yet)

Also add options to explicitly enable or disable some of these files
- YCM_USE_CMAKE_2_8_8 [ON] (only if cmake <= v2.8.7)
- YCM_USE_CMAKE_2_8_12 [ON] (only if cmake <= v2.8.11.2)
- YCM_USE_CMAKE_NEXT [ON]
- YCM_USE_CMAKE_PROPOSED [OFF]

The variable YCM_MODULE_PATH is populated so that newer files
are found earlier by CMake.
CMakeParseArguments.cmake: Import from CMake git

(ref 6d1444feacb1c2d621b776ac61412f92ff0a1c34)
CMakeParseArguments: Handle empty arguments
GazeboYARPPlugins: Update repository address
CMake 2.8.13 won't exist, it will be 3.0.0
Use unset(foo) instead of set(foo )
YCMEPHelper: Use patched CMakeParseArguments properly
Add workaround for set(var "" PARENT_SCOPE) unsetting variables