FIX: Strict error warnings on DataExtension

PHP is throwing strict error warnings when overriding the
updateCMSFields and other functions in custom DataExtensions due to
the fact that the abstract class doesn't declare the variables should
be passed by reference
FIX: validate doesn't take var by reference

Got a bit carried away, validate doesn't take the var by reference
Merge pull request #1156 from mandrew/patch-1

FIX: Strict error warnings on DataExtension
FIX Don't escape values on TreeDropdownField readonly views

They typically output TreeTitle() which is assumed to be HTML.
Revert "FIX: Strict error warnings on DataExtension"
This reverts commit 1960df8bc30ecb0467a33275810fd121a0125733.

Revert "FIX: validate doesn't take var by reference"
This reverts commit 866bb0713b9918e0450a516da9b7662c3287e24f.

@ajshort has changed the method signatures in 1f6f7f08. While it wasn't explicitly noted in the commit message, I think its a good change - objects like a FieldList are always passed by reference in PHP, no need to declare that behaviour.
Incorrect Contant-Type header for RSS feeds

It should be application/rss+xml but not text/xml.
FEATURE: Added ability to query size of Varchar

This allows a developer to programatically access the size of the DB Varchar field. This allows us to be a bit more DRY and to define the size in one place and limit TextFields to the same value
Merge pull request #1162 from dhensby/patch-1

NEW Add Varchar::getSize()
Update admin/javascript/lang/de_DE.js

fixed typo in translation
Merge pull request #1163 from schwarz-computer-systeme/3.0

Update admin/javascript/lang/de_DE.js
Removed explicit pass-by-ref in DataExtension->validate()

Same fix as be97535b for 3.1. Makes the method signature
more consistent with other DataExtension methods,
and comply with its subclass implementation in
Hierarchy->validate(). See accbd7f1e2 for more comments.
FIX Group->canEdit() correct non-admin checks (fixes #8250)

Due to changed return value of DataObject::get(),
the (negated) check always returned false.
This wasn't noticed in 3.0 because Group->canEdit() is rarely
enforced, but does become noticeable in 3.1 where GridField
checks those object-level permissions.

Thanks to @purplespider for reporting!
Merge pull request #1160 from uniun/patch-3

Incorrect Contant-Type header for RSS feeds