fix fs#428

[[Imported from SVN: r5294]]

doc/buildsystem/buildsystem.tex

@@ -73,8 +73,8 @@ Im Neuenheimer Feld 368, D-69120 Heidelberg, Germany}\\
 \item \texttt{dune-fem}
 \end{itemize}
 
-These modules interact very tightly and depend on each
-other.
+Single modules can depend on other modules and so the \dune modules
+build a dependency graph.
 
 The build system is structured as follows:
 \begin{itemize}