Fix false positive in mailmotor subscribe/unsubscribe actions

When the subscribe or unsubscribe function fails and returns false, the
error should be triggered. Otherwise the end-user gets a false positive
success message.

This should fix ticket #336
html entity decoding in link list

The editor plugin that enables selecting an internal link gets
unreadable if ampersands or quotes are used in a page title, because
they are stored encoded.

For the link list, I believe this is not necessary. By decoding the
titles, the link list is much more usable by end users.
Use SpoonFilter to decode html entities
Merge pull request #360 from PeterMuusers/master

Fix false positive mailmotor subscribe/unsubscribe result