Original implementation of authorship test assumed a simple pad reload
would switch the author -- and it actually did on Chrome. But other
browsers might keep the author id on cookie.
To force the author switch, expire the cookie before reloading the pad.
Fixes: #3435
When comparing original content with the changes made by the user, we
need to ignore some line attribs that are added by content collector,
otherwise we would consider the change started on the first char of the
line -- the '*' that is added when line has line attribs.
In order to be able to handle both #3354 and #3118, we need to take into
account both the styles attribs (to fix#3354) and the line attribs
defined by any of the plugins (to fix#3118), but we can ignore those
extra line attribs that are added by Etherpad and do not add any
functionality (`'lmkr', 'insertorder', 'start'`).
