Included *.vtp Files for tarball

reviewed and discussed with Alex

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@13507 2fb0f335-1f38-0410-981e-8018bf24f1b0

test/references/Makefile.am

 referencesdir = $(includedir)/test/references
-EXTRA_DIST:=$(wildcard *.vtu)
+EXTRA_DIST:=$(wildcard *.vtu) $(wildcard *.vtp)
 
 include $(top_srcdir)/am/global-rules