[BUGFIX] Sending fails on multiple email-addresses

Specifying multiple recipients (To or CC) for emails
leads to an error upon form-submit without further explanation.
This patch implements validation for multiple email addresses of
which only the valid ones are then returned.
The sending-API can already handle multiple recipients.

Change-Id: I59b65adc4e09d298167738778c17d310b8ecce47
Fixes: #44485
Releases: 4.7, 6.0, 6.1
Reviewed-on: https://review.typo3.org/17505
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Tested-by: Stefan Neufeind
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert
[TASK] Detect APC and APCu correctly

APCu is just the user-data part of APC,
providing the same API.

If installed it currently identifies itself
as both "apcu" and "apc" (for compatibility).
Thus if "apcu" shows up, we actually have an APC
without opcache-support.

Resolves: #46821
Releases: 4.5, 4.7, 6.0, 6.1
Change-Id: Ie046fa21102c5c7eb6b5b8a9cf54b20252c30cd9
Reviewed-on: https://review.typo3.org/19462
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
[BUGFIX] Fix of Close-button in flash messages

The close button did not work because hide() was called on
a HTMLElement instead of an Ext.Element.

Fixes: #46373
Related: #31368
Releases: 6.1, 6.0, 4.7
Change-Id: I70c65a82683ece39de4ed043a916b0521aabafa1
Reviewed-on: https://review.typo3.org/19252
Tested-by: Wouter Wolters
Reviewed-by: Laurent Cherpit
Tested-by: Laurent Cherpit
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn