Fixes listcommands; status 500 error

Some people with really long names are getting a status 500 error on listcommands (http://chat.stackoverflow.com/transcript/message/13154994#13154994), because a 20 char buffer zone is not enough. This patch fixes that (http://chat.stackoverflow.com/transcript/message/13155861#13155861), by taking username lengths into account. `pagination.length` adds an extra 4 char buffer zone (counting the brackets), so we should be good, up to 1,000 commands.