Find* (and some other): use ${CMAKE_CURRENT_LIST_DIR} in include()

This solves a lots of warnings, e.g. in the FindModulesExecuteAll test. If the
installed version on the system is rather old this may even lead to bugs, e.g.
https://bugs.gentoo.org/show_bug.cgi?id=436540

Modules/FindOpenSceneGraph.cmake

@@ -72,7 +72,7 @@
 #  Output variables of the form OPENSCENEGRAPH_FOO
 #
 
-include(Findosg_functions)
+include(${CMAKE_CURRENT_LIST_DIR}/Findosg_functions.cmake)
 
 set(_osg_modules_to_process)
 foreach(_osg_component ${OpenSceneGraph_FIND_COMPONENTS})