default: make 'self.download' use url&md5sum options if called without url

README.rst

@@ -27,7 +27,7 @@ Example that installs software::
   url = http://host/path/foo.tar.gz
   md5sum = ...
   install =
-    extract_dir = self.extract(self.download(options['url'], options['md5sum']))
+    extract_dir = self.extract(self.download())
     self.copyTree(guessworkdir(extract_dir), location)
     ${:update}
   update =

slapos/recipe/build/__init__.py

@@ -143,6 +143,8 @@ class Script(EnvironMixin):
           '\n  '.join(promise_problem_list))
 
   def download(self, *args, **kw):
+    if not (args or 'url' in kw):
+        args = self.options['url'], self.options.get('md5sum') or None
     path, is_temp = zc.buildout.download.Download(self.buildout['buildout'],
       hash_name=True)(*args, **kw)
     if is_temp: