Marks the new arpack cmake modules for installation.

The new modules from the arpack feature branch were
never installed and this would have broken installed dune-istl
modules.

With this commit they now are installed for both CMAke and autotools.

cmake/modules/CMakeLists.txt

 set(modules
+  AddARPACKPPFlags.cmake
   AddSuperLUFlags.cmake
   DuneIstlMacros.cmake
+  FindARPACK.cmake
+  FindARPACKPP.cmake
   FindSuperLU.cmake)
 
 install(FILES ${modules} DESTINATION

cmake/modules/Makefile.am

-MODULES = AddSuperLUFlags.cmake \
+MODULES = AddARPACKPPFlags.cmake \
+ AddSuperLUFlags.cmake \
  DuneIstlMacros.cmake \
+ FindARPACK.cmake \
+ FindARPACKPP.cmake \
  FindSuperLU.cmake
 
 modulesdir= $(datadir)/dune/cmake/modules