Buildsystem: Clean up the revision.h target generation

- rename src/revision.h folder to src/genrev
- ensure BUILDDIR/revision.h file is cleared/removed before generation (deleted/recreated during buildmode-changes)
Note: This needs further testing, so please give feedback.

--HG--
branch : trunk
rename : src/revision.h/CMakeLists.txt => src/genrev/CMakeLists.txt

cmake/genrev.cmake

@@ -67,4 +67,3 @@ configure_file(
   "${BUILDDIR}/revision.h"
   @ONLY
 )
-message(STATUS "Created revision.h")