improve clean for auto-generated sources.list

vendor/debian/makefile

@@ -10,6 +10,8 @@ doc binary manpages: sources.list
 sources.list: sources.list.in ../../doc/apt-verbatim.ent
 	sed -e 's#&stable-codename;#$(shell ../getinfo debian-stable-codename)#g' $< > $@
 
-clean:
+clean: clean/sources.list
+
+clean/sources.list:
 	rm -f sources.list
 

vendor/raspbian/makefile

@@ -10,5 +10,7 @@ doc binary manpages: sources.list
 sources.list: sources.list.in ../../doc/apt-verbatim.ent
 	sed -e 's#&stable-codename;#$(shell ../getinfo debian-stable-codename)#g' $< > $@
 
-clean:
+clean: clean/sources.list
+
+clean/sources.list:
 	rm -f sources.list

vendor/steamos/makefile

@@ -10,6 +10,8 @@ doc binary manpages: sources.list
 sources.list: sources.list.in ../../doc/apt-verbatim.ent
 	sed -e 's#&stable-codename;#$(shell ../getinfo debian-stable-codename)#g' $< | sed -e 's#&steamos-codename;#$(shell ../getinfo current-distro-codename)#g' > $@
 
-clean:
+clean: clean/sources.list
+
+clean/sources.list:
 	rm -f sources.list
 

vendor/ubuntu/makefile

@@ -10,5 +10,7 @@ doc binary manpages: sources.list
 sources.list: sources.list.in ../../doc/apt-verbatim.ent
 	sed -e 's#&ubuntu-codename;#$(shell ../getinfo ubuntu-codename)#g' $< > $@
 
-clean:
+clean: clean/sources.list
+
+clean/sources.list:
 	rm -f sources.list