Bug 1232171 - 'make clean' shouldn't delete rst/, images/ and Makefile, only generated files

docs/en/Makefile

@@ -39,7 +39,7 @@ help:
 	@echo "  doctest    to run all doctests embedded in the documentation (if enabled)"
 
 clean:
-	-rm -rf $(BUILDDIR)/*
+	find $(BUILDDIR) -maxdepth 1 -type d -not -name rst -not -name images -not -name . -exec rm -rf {} \;
 
 html:
 	$(SPHINXBUILD) -b html $(ALLSPHINXOPTS) $(BUILDDIR)/html