Update the dune-elasticity build system some more

.gitignore

-
-# /
-/Makefile
-/Makefile.in
-/config.*
-/configure
-/dependencies.m4
-/aclocal.m4
-/autom4te.cache
-/depcomp
-/install-sh
-/missing
-/mkinstalldirs
-/libtool
-/dune.pc
-/semantic.cache
-/stamp-h1
-/html
-/.deps
-/.libs
-/am
-/linelast
-/nonlinelast
-
-# /dune/
-/dune/Makefile.in
-/dune/Makefile
-
-# /dune/elasticity/
-/dune/elasticity/Makefile.in
-/dune/elasticity/Makefile
-/dune/elasticity/semantic.cache
-
-# /dune/elasticity/assemblers/
-/dune/elasticity/assemblers/Makefile
-/dune/elasticity/assemblers/Makefile.in
-
-# /dune/elasticity/common/
-/dune/elasticity/common/Makefile
-/dune/elasticity/common/Makefile.in
-
-# /dune/elasticity/estimators/
-/dune/elasticity/estimators/Makefile
-/dune/elasticity/estimators/Makefile.in
-
-# /dune/elasticity/materials/
-/dune/elasticity/materials/Makefile
-/dune/elasticity/materials/Makefile.in
-
-# /m4/
-/m4/Makefile.in
-/m4/Makefile
-
-# /test/
-/test/.deps
-/test/.libs
-/test/Makefile
-/test/Makefile.in
-/test/semantic.cache
+# ignore backup files
+*~
 
 # Default cmake build directory
 /build-cmake