Core changes for AbuseFilter extension.

In particular:
Xml.php
* Add textarea method to Xml class.
* Make submit button optional for Xml::buildForm
* Right-align labels in buildForm.

Article.php:
* Make ArticleDelete hook display a real error

EditPage.php:
* Split off getBaseRevision()

Title.php:
* Allow errors to be ignored to be sent to getUserPermissionsErrors.
* Allow AbortMove hook to display a real error.

Block.php:
* Add 'mAngryAutoblock' option, for blocks by software, which does retroactive autoblocks on the last 5 IPs used in the last 7 days.