Use ecm_configure_package_config_file instead of configure_file

Works better on all kind of systems (in concrete it fixes things for Debian
users)

CMakeLists.txt

@@ -507,7 +507,9 @@ add_subdirectory(autotests)
 add_subdirectory(tests)
 add_subdirectory(doc)
 
-configure_file(KWinDBusInterfaceConfig.cmake.in "${CMAKE_CURRENT_BINARY_DIR}/KWinDBusInterfaceConfig.cmake" @ONLY)
 set(CMAKECONFIG_INSTALL_DIR "${CMAKECONFIG_INSTALL_PREFIX}/KWinDBusInterface")
+ecm_configure_package_config_file(KWinDBusInterfaceConfig.cmake.in
+    "${CMAKE_CURRENT_BINARY_DIR}/KWinDBusInterfaceConfig.cmake"
+    INSTALL_DESTINATION ${CMAKECONFIG_INSTALL_DIR})
 install(FILES ${CMAKE_CURRENT_BINARY_DIR}/KWinDBusInterfaceConfig.cmake
     DESTINATION ${CMAKECONFIG_INSTALL_DIR})

KWinDBusInterfaceConfig.cmake.in

@@ -1,4 +1,4 @@
-get_filename_component(PACKAGE_PREFIX_DIR "${CMAKE_CURRENT_LIST_DIR}/../../../" ABSOLUTE)
+@PACKAGE_INIT@
 
 set(KWIN_INTERFACE "${PACKAGE_PREFIX_DIR}/@DBUS_INTERFACES_INSTALL_DIR@/org.kde.KWin.xml")
 set(KWIN_COMPOSITING_INTERFACE "${PACKAGE_PREFIX_DIR}/@DBUS_INTERFACES_INSTALL_DIR@/org.kde.kwin.Compositing.xml")