[TASK] Collection of unofficial fixes

Fixes that are not meant to be commited to the core or are custom
workarounds for specific problems:

Tables starting with user_piwikintegration_ are ignored in the install
tool schema comparator.

The $isModified property of the ObjectStorage is set to TRUE by
default to fix problems with non persisted changes.

The handling of union statements for ORDER BY usage in the
Typo3DbBackend is improved.

The form.errors view helper merges all property errors.

Change-Id: I91a37be041637d2779178355530dde3f27be5a7f