Make documentation consistent with code.

slapos/libnetworkcache.py

@@ -202,7 +202,7 @@ class NetworkcacheClient(object):
 
   def select(self, key):
     ''' Download a file from shacache by selecting the entry in shadir
-    Raise DirectoryNotFound if multiple files are found.
+    Raise DirectoryNotFound if no trustable file is found.
     '''
     url = os.path.join(self.shadir_url, key)
     request = urllib2.Request(url=url, data=None,