ENH: First step of install script generator cleanup.  Each configuration to be installed is now separately handled instead of using variables to store per-configuration names.  For targets the component and configuration install-time tests are now done in the install script instead of in the FILE(INSTALL) command.  This cleans things up like not trying to strip a file that was optionally not installed.  It also simplifies the code for install_name adjustment on OSX.  This commit is surrounded by the tags CMake-InstallGeneratorCleanup1-pre and CMake-InstallGeneratorCleanup1-post.