build system: remove directories created by tests in "make clean"

These extra directories cause problems for building on Debian
twice in a row.

In order to remove directories, we need to us "rm -rf" instead of
"rm -f". So now we should be extra careful what we add to the
variable CLEAN.

Makefile.local

@@ -265,7 +265,7 @@ quiet ?= $($(shell echo $1 | sed -e s'/ .*//'))
 
 .PHONY : clean
 clean:
-	rm -f $(CLEAN); rm -rf .deps
+	rm -rf $(CLEAN); rm -rf .deps
 
 # We don't (yet) have any distributed files not in the upstream repository.
 # So distclean is currently identical to clean.

test/Makefile.local

@@ -31,4 +31,5 @@ check: test
 SRCS := $(SRCS) $(smtp_dummy_srcs)
 CLEAN := $(CLEAN) $(dir)/smtp-dummy $(dir)/smtp-dummy.o \
 	 $(dir)/symbol-test $(dir)/symbol-test.o \
-	 $(dir)/arg-test $(dir)/arg-test.o
+	 $(dir)/arg-test $(dir)/arg-test.o \
+	 $(dir)/corpus.mail $(dir)/test-results $(dir)/tmp.*