[autotools] Fix wildcard stuff in doc/handbook.

Make complained about an empty variable. Probably it did
not like the :=+, thus it was replaced by " \" and
everything is added in one line.
(reviewed by fetzer)


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@13341 2fb0f335-1f38-0410-981e-8018bf24f1b0

doc/handbook/Makefile.am

@@ -11,8 +11,8 @@ CURDIR=doc/handbook
 handbookdir=$(docdir)/handbook
 handbook_DATA = dumux-handbook.pdf
 
-CLEANFILES := $(wildcard *.aux) $(wildcard *.bbl) $(wildcard *.blg) $(wildcard *.log) $(wildcard *.out) $(wildcard *.toc) $(wildcard *.dvi) $(wildcard *.ps)
-CLEANFILES +:= $(wildcard *.4ct) $(wildcard *.4tc) $(wildcard *.css) $(wildcard *.idv) $(wildcard *.idx) $(wildcard *.lg) $(wildcard *.tid) $(wildcard *.tmp) $(wildcard *.tms) $(wildcard *.xref)
+CLEANFILES := $(wildcard *.aux) $(wildcard *.bbl) $(wildcard *.blg) $(wildcard *.log) $(wildcard *.out) $(wildcard *.toc) $(wildcard *.dvi) $(wildcard *.ps) \
+  $(wildcard *.4ct) $(wildcard *.4tc) $(wildcard *.css) $(wildcard *.idv) $(wildcard *.idx) $(wildcard *.lg) $(wildcard *.tid) $(wildcard *.tmp) $(wildcard *.tms) $(wildcard *.xref)
 CLEANFILES += $(DOCS)
 
 doc: $(TEXSOURCE)