build: more out-of-tree fixups

- clear the __pycache__ during 'make clean'
- Copy the qrc locale file to a temp location and remove it when finished
  (rcc expects everything to be in the same path)

src/Makefile.am

@@ -441,6 +441,7 @@ clean-local:
 	-$(MAKE) -C univalue clean
 	-rm -f leveldb/*/*.gcda leveldb/*/*.gcno leveldb/helpers/memenv/*.gcda leveldb/helpers/memenv/*.gcno
 	-rm -f config.h
+	-rm -rf test/__pycache__
 
 .rc.o:
 	@test -f $(WINDRES)