[cmake] extract bottom block from config.h.cmake

For dune-grid a bottom section is needed to place the Grid Type magic at the bottom of the config.h
file in derived modules.

In this patch a /* begin bottom */ ... /* end bottom */ block from each module's config.h.cmake file is extracted and placed
at the end of the collected config.h file.

This resolves the problems from FS#1713.

cmake/modules/DuneMacros.cmake

@@ -754,7 +754,18 @@ macro(dune_regenerate_config_cmake)
          ".*/\\*[ ]*begin[ ]+${_dep}[^\\*]*\\*/(.*)/[/\\*][ ]*end[ ]*${_dep}[^\\*]*\\*/" "\\1"
          _tfile "${_file}")
        # strip the private section
-       string(REGEX REPLACE "(.*)/[\\*][ ]*begin private.*/[\\*][ ]*end[ ]*private[^\\*]\\*/(.*)" "\\1\\2" _file "${_tfile}")
+       string(REGEX REPLACE "(.*)/[\\*][ ]*begin private.*/[\\*][ ]*end[ ]*private[^\\*]\\*/(.*)" "\\1\\2" _ttfile "${_tfile}")
+
+       # extract the bottom section
+       string(REGEX MATCH "/[\\*][ ]*begin bottom.*/[\\*][ ]*end[ ]*bottom[^\\*]\\*/" _tbottom "${_ttfile}")
+       string(REGEX REPLACE ".*/\\*[ ]*begin[ ]+bottom[^\\*]*\\*/(.*)/[/\\*][ ]*end[ ]*bottom[^\\*]*\\*/" "\\1" ${_dep}_CONFIG_H_BOTTOM "${_tbottom}" )
+       string(REGEX REPLACE "(.*)/[\\*][ ]*begin bottom.*/[\\*][ ]*end[ ]*bottom[^\\*]\\*/(.*)" "\\1\\2" _file  "${_ttfile}")
+
+       # append bottom section
+       if(${_dep}_CONFIG_H_BOTTOM)
+         set(CONFIG_H_BOTTOM "${CONFIG_H_BOTTOM} ${${_dep}_CONFIG_H_BOTTOM}")
+       endif()
+
        file(APPEND ${CONFIG_H_CMAKE_FILE} "${_file}")
      endif(EXISTS ${_mod_conf_file})
    endforeach()
@@ -762,6 +773,10 @@ macro(dune_regenerate_config_cmake)
  # parse again dune.module file of current module to set PACKAGE_* variables
  dune_module_information(${CMAKE_SOURCE_DIR} QUIET)
  file(APPEND ${CONFIG_H_CMAKE_FILE} "\n${_myfile}")
+ # append CONFIG_H_BOTTOM section at the end if found
+ if(CONFIG_H_BOTTOM)
+    file(APPEND ${CONFIG_H_CMAKE_FILE} "${CONFIG_H_BOTTOM}")
+ endif()
 endmacro(dune_regenerate_config_cmake)
 
 # macro that should be called at the end of the top level CMakeLists.txt.