add no-documentation tag to dist when build docs is disabled.

[[Imported from SVN: r5024]]

doc/Makefile.am

@@ -24,8 +24,16 @@ EXTRAINSTALL=example.opts
 # install the html pages
 docdir=$(datadir)/doc/dune-common
 doc_DATA = $(PAGES) example.opts
+
 EXTRA_DIST = $(PAGES) example.opts
 
+if ! BUILD_DOCS
+# add tag to notify that dist has been build without documentation
+dist-hook:
+	echo "# No documentation included in distribution! " > $(distdir)/$(DOCUMENTATION_TAG_FILE)
+endif
+
+
 # include rules for wml -> html transformation
 include $(top_srcdir)/am/webstuff