Fix problems with CLEANFILES and automake-1.11.1

Running with automake-1.11.1, a couple fixes are needed
for CLEANFILES when gtk-doc is not installed.

(Found with Amazon Linux AMI release 2012.03)

https://bugzilla.gnome.org/show_bug.cgi?id=682067

autogen.sh

@@ -11,7 +11,10 @@ GTKDOCIZE=$(which gtkdocize 2>/dev/null)
 if test -z $GTKDOCIZE; then
         echo "You don't have gtk-doc installed, and thus won't be able to generate the documentation."
         rm -f gtk-doc.make
-        echo 'EXTRA_DIST =' > gtk-doc.make
+        cat > gtk-doc.make <<EOF
+EXTRA_DIST =
+CLEANFILES =
+EOF
 else
         gtkdocize || exit $?
 fi

glib/Makefile.am

@@ -84,7 +84,7 @@ EXTRA_DIST += 			\
 	gconstructor.h		\
 	$(MIRRORING_TAB_SOURCE)
 
-CLEANFILES= libglib-gdb.py
+CLEANFILES += libglib-gdb.py
 
 # These may be in the builddir too
 BUILT_EXTRA_DIST = 		\