API Remove Content-Length setting from HTTPResponse (fixes #8010)

This reverts commit 356a367eb5d05bea3dfa2edaeabc52a2496b93b2.
We can't use headers_sent() to determine an accurate
content length, since PHP defaults to buffering a couple of bytes
even without ob_start() (see "output_buffering" setting).
This makes the patch harmful, since it breaks any responses relying
on more structure data, like removing closing brackets from JSON.
Which in turn breaks the CMS in horrible ways (see #8010).
See #7574 for context.
API: Use HTMLText as default for RSS Description

To allow for custom RSS descriptions (i.e. provided by a method rather than a DB field) and avoid double escaping a better default class for Description is 'HTMLText'. http://www.silverstripe.org/customising-the-cms/show/11606#post319519
Consistently exposed ManyManyList information through getters.
FIX Node updates in IE without non-object error

Bug was most prominent after page publication,
which triggers a node reload. It iterated through
all node attributes to assign them to the existing node,
which apparently includes some non-scalar attributes
that can't simply be copied in IE.
Merge pull request #1123 from chillu/pulls/revert-content-length

API Remove Content-Length setting from HTTPResponse (fixes #8010)
Include "media" attr for module customCSS() (fixes #8219)
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.
Trigger delete confirmation popup when deleting a GridFieldDetailForm record
Merge pull request #1158 from halkyon/deleteaction

Trigger delete confirmation popup when deleting a GridFieldDetailForm re...
NEW Don't load CMS preview iframe if not visible (fixes #8247)
Fixed DatetimeField formatting (single row, smaller field)

Also removed the arbitrary right-floating of fields within a fieldgroup
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()
API Removed 'BadLoginURL' session var from MemberLoginForm

It was never set in core, and is generally undocumented,
hence just unnecessarily increases the security surface
of this sensitive class.
DataObject on*() callbacks now consistently invoke on subclasses as well

Before this was only possible for some specific ones, like onBeforeWrite.
This excludes any callbacks with augment*() or update*() naming,
since these are assumed to be on extension only, with a corresponding
base method available on the class itself (e.g. "updateCMSFields()"
vs "getCMSFields()").