morebits: fix handling of hard errors

[siddharthvp]

In #1179, support for new error formats were added and used by default. However, the error handling code still assumes the legacy errorformat, which passes details of the first error, while in the newer ones we have an array errors.

Notes for testing:
On testwiki, add text "Trigger abuse filter warn" to any page (it triggers https://test.wikipedia.org/wiki/Special:AbuseFilter/256):

var p = new Morebits.wiki.page('SD0001test', '');
p.setAppendText('trigger abuse filter warn');
p.setEditSummary('edit summary');
p.append();

Without this patch, we get:

The TypeError prevents any failure handling callback from running (one of the reasons why the callback approach is sub-optimal and we should be using promises everywhere).

[siddharthvp]

Originally reported by User:Sdkb at https://en.wikipedia.org/wiki/User_talk:SD0001/DYK-helper#Bug:_Loses_nomination_when_edit_filter_triggered (DYK-helper uses morebits)

[siddharthvp]

Merged; clear-cut bug affecting users