[cmake,release] Install cmake macros to $(datadir)/dune/cmake/

Previously, the macros were installed to $(datadir)/cmake/. As we have
some macros in DUNE that might also be in other packages
this may cause conflicts in package managers. With this patch we install
them to $(datadir)/dune/cmake to resolve this issue. Together with the
last patch this will resolve problems  outlined in flyspray
task 813
https://dune-project.org/flyspray/index.php?do=details&task_id=813
I apologize for givin the wrong task number in the previous patch.

cmake/modules/DuneMacros.cmake

@@ -526,7 +526,7 @@ macro(dune_project)
   if(NOT DUNE_INSTALL_MODULEDIR)
     set(DUNE_INSTALL_MODULEDIR ""
       CACHE PATH
-      "Installation directory for CMake modules. Default is \${CMAKE_INSTALL_DATAROOTDIR}/cmake/modules when not set explicitely")
+      "Installation directory for CMake modules. Default is \${CMAKE_INSTALL_DATAROOTDIR}/dune/cmake/modules when not set explicitely")
     set(DUNE_INSTALL_MODULEDIR ${CMAKE_INSTALL_DATAROOTDIR}/cmake/modules)
   endif(NOT DUNE_INSTALL_MODULEDIR)
 
@@ -600,7 +600,7 @@ macro(finalize_dune_project)
   include(CMakePackageConfigHelpers)
   include(GNUInstallDirs)
   set(DOXYSTYLE_DIR ${CMAKE_INSTALL_DATAROOTDIR}/dune-common/doc/doxygen/)
-  set(SCRIPT_DIR ${CMAKE_INSTALL_DATAROOTDIR}/cmake/scripts)
+  set(SCRIPT_DIR ${CMAKE_INSTALL_DATAROOTDIR}/dune/cmake/scripts)
 
   if(NOT EXISTS ${PROJECT_SOURCE_DIR}/cmake/pkg/${DUNE_MOD_NAME}-config.cmake.in)
     # Generate a standard cmake package configuration file

cmake/modules/Makefile.am

@@ -28,7 +28,7 @@ MODULES = \
   UseInkscape.cmake       \
   UseLATEX.cmake
 
-modulesdir = $(datadir)/cmake/modules
+modulesdir = $(datadir)/dune/cmake/modules
 dist_modules_DATA = ${MODULES}
 
 include $(top_srcdir)/am/global-rules

cmake/scripts/CMakeLists.txt

@@ -6,4 +6,4 @@ set(modules
   RunDoxygen.cmake)
 
 install(FILES ${modules} ${CMAKE_CURRENT_SOURCE_DIR}/BuildTests.cmake.in
-  DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/cmake/scripts)
+  DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/dune/cmake/scripts)

cmake/scripts/Makefile.am

@@ -5,7 +5,7 @@ MODULES = BuildTests.cmake.in \
   InstallFile.cmake           \
   RunDoxygen.cmake
 
-modulesdir = $(datadir)/cmake/scripts
+modulesdir = $(datadir)/dune/cmake/scripts
 dist_modules_DATA = ${MODULES}
 
 include $(top_srcdir)/am/global-rules