learn to not download UIDs defined by the user

Allow users to workaround offending emails that offlineimap can't download.

Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap.conf

@@ -1187,6 +1187,17 @@ remoteuser = u"username"
 #"cvlc --play-and-stop --play-and-exit /path/to/sound/file.mp3 > /dev/null 2>&1")
 
 
+# This option stands in the [Repository RemoteExample] section.
+#
+# If offlineiamp is having troubles to download some UIDS, it's possible to get
+# them ignored in a list.
+#
+# The function must return the list of UIDs to ignore, None otherwise. It is
+# passed the folder name.
+#
+#copy_ignore_eval = lambda foldername: {'INBOX': [2, 3, 4]}.get(foldername)
+
+
 [Repository GmailExample]
 
 # A repository using Gmail's IMAP interface.