adjust screen output to reflect the fact that now UG and AmiraMesh do need to...

adjust screen output to reflect the fact that now UG and AmiraMesh do need to be found by the build system if you want to use them in your applications

[[Imported from SVN: r2114]]

configure.ac

@@ -112,9 +112,10 @@ fi
 AC_SUBST(AM_CPPFLAGS)
 
 echo
-echo Note: the libraries checked for above are only used for the self-test of Dune.
-echo The library itself will build and the headers will work even if
-echo Albert, UG, Amiramesh, MPI, etc. cannot be found.
+echo Note: Most of the libraries checked for above are only used for the self-test
+echo of Dune.  The library itself will build and the headers will work even if
+echo Albert, MPI, etc. cannot be found.  An exception to this are UG and AmiraMesh
+echo which need to be found right now if you want to use them later.
 echo
 
 # write output