Move mail system classes from system.mail.inc to PSR-0 classes in Drupal\Core

I had a small problem with this patch, about not being able to define a Default class in Drupal\Core\Mail because of PHP restrictions, so in lack of any better name, I renamed the default class to.. *drumroll*.. Mail :) Basically, DefaultMailSystem is now Drupal\Core\Mail\Mail.

I suppose we want to leave further clean-up of mail.inc to another issue? I'm thinking of a base class (abstract?) that will hold all the underscored functions that now reside in mail.inc.

Sigh..

+++ b/core/lib/Drupal/Core/Mail/Mail.php
@@ -2,20 +2,23 @@
+class Mail implements MailInterface {

Yeah, I agree, silly name. :-) Could we perhaps call this something descriptive, like Sendmail, or PhpMail?

We don't have a Drupal\Core\Cache\Cache class for the default, we have a Drupal\Core\Cache\Database class for the default. That is more descriptive.

+++ b/core/lib/Drupal/Core/Mail/Testing.php
@@ -0,0 +1,30 @@
+class Testing extends Mail implements MailInterface {

This may not be the place to make this change, but "Testing" is a bad name for this class. It documents what it is often used for, not what it does. It should rather be something like VariableLog.

This looks good otherwise on visual inspection. Is there another inc file we can kill in the process? :-)

20 days to next Drupal core point release.

I like PhpMail and VariableLog, so went ahead with those names. Interdiff is against #3.

The only inc file left is mail.inc, which still contains some procedural stuff, but I think converting that to OO deserves a new issue.

I'm satisfied with #5, but it should probably get a second set of eyes on it before it goes RTBC.

Rerolled for the system.info fail.