remove covers/ directory when performing 'make clean'

- this directory is (fastly) auto generated during 'make' anyway
- it avoids songbooks displaying out of date covers

macos/clean.sh

@@ -2,3 +2,5 @@
 #
 echo "manually performs 'make clean'"
 rm -rf *.aux *.d *.toc *.out *.log *.nav *.snm *.sbx *.sxd
+echo "remove temporary covers"
+rm -rf covers/

makefile

@@ -61,6 +61,7 @@ clean:
 	       $(TARGETS:%=%.nav) $(TARGETS:%=%.snm)
 	@rm -f *.sbx *.sxd *.sxc
 	@rm -f *.pyc
+	@rm -rf covers/
 
 cleanall: clean
 	@rm -f $(PDF)

windows/clean.bat

@@ -1,2 +1,4 @@
 Rem manually performs "make clean"
 FOR %%A IN (*.aux *.d *.toc *.out *.log *.nav *.snm *.sbx *.sxd) DO DEL %%A
+Rem remove temporary covers
+FOR %%A IN (covers\*.*) DO DEL %%A