Using Return-Path email address in MAIL FROM instead of a header in SmtpTransport.

The Return-Path header should not be present on the SMTP transaction, this header is set by the time of final delivery.
Quote RFC2821:
> When the delivery SMTP server makes the "final delivery" of a message, it inserts a return-path line at the beginning of the mail data. This use of return-path is required; mail systems MUST support it. The return-path line preserves the information in the from the MAIL command.
Unify modified/created times

The former implementation meant that it was not guarantee that
the times automatically generated for the modified/created fields
would be exactly the same for a given operation.
Merge pull request #1348 from thomseddon/consistent-timestamps

Unify modified/created times. Both the created/updated timestamps will reflect the same point in time now.
doc block formhelper postLink
Merge pull request #1350 from dereuromark/master-post-link-doc-block

doc block formhelper postLink
Merge pull request #1334 from thegallagher/2.3-cache-fix

Fix content-type header in cached views.

Fixes #2358
Remove dead view cache code.

Now that cache files contain the response headers, this is no longer
needed. Remove what is now duplicate code.

Refs #2358
Merge pull request #1349 from renansaddam/smtpTransportReturnPath

Using Return-Path email address in MAIL FROM instead of a header in SmtpTransport
duplicate line removed
Remove undocumented magic features for IIS.

Undocumented, untested features break very easily. It is best to not
have them where possible.
Merge pull request #1327 from pafuinlu/patch-2

Added a clear() function to Model.php (2.4 branch)
Add tests for Model::clear()
Fix incorrect autolinking when urls end at HTML tags.

Fixes #3879
Merge branch 'master' into 2.4
AuthComponent: Allow suppressing authError message

When unauthenticated users accesses protected areas, they are greeted
with the default 'You are not allowed to access that location' which is
not desired in some cases.

This patch allows applications to suppress this message by setting
AuthComponent::authError to false bypassing the call to
SessionComponent::setFlash() altogether.

Refs: https://github.com/croogo/croogo/pull/175#discussion_r4714240
assert proper array access for _dateTimeSelected()
CakeSession improvements
Merge pull request #1361 from dereuromark/master-form-helper-datetime

assert proper array access for _dateTimeSelected()
Merge pull request #1362 from dereuromark/master-cake-session

cake session clarification
Fix to the date input year field

Create the field if no value is informed only to the maxYear and not to
the current date.