Add a new directory parallel that will take the parallel index set stuff from dune-istl

[[Imported from SVN: r6257]]

dune/common/parallel/Makefile.am

+# $Id$
+
+SUBDIRS =
+
+parallelincludedir = $(includedir)/dune/common/parallel
+parallelinclude_HEADERS =
+
+include $(top_srcdir)/am/global-rules