e.g. ' should be treated like the ascii apostrophe '
http://musicbrainz.org/search/textsearch.html?query=John%27s&type=artist&limit=25&handlearguments=1
http://musicbrainz.org/search/textsearch.html?query=John%E2%80%99s&type=artist&limit=25&handlearguments=1

and in ngs:
http://test.musicbrainz.org/search?query=John%27s&type=artist&limit=25
http://test.musicbrainz.org/search?query=John%E2%80%99s&type=artist

there are probably more but I don't have any examples, I'll ask people to comment on this ticket if they can find some