Messed up Mailer (Introduced by 4.1 -> 4.2)

In 4.1 it was possible returning a count of sent emails from Mail::send().
In 4.2 you'll always get null returned. (Because Mail::send() is now returning the void method `sendSwiftMessage()`)

(`sendSwiftMessage()` was returning the count in  4.1 ...)


If that was intended the send method needs an update which I'm providing with this pull request.
Anyways I hope it was not and the send() method will return the count of sent emails again in future. (Was using this feature and liked it alot)
Add isPretending()
Update readme.md contributing from 4.1 to 4.2

Small quick change of reference to keep readme.md current.
Merge pull request #4749 from riotCode/patch-2

Update readme.md contributing from 4.1 to 4.2
Merge pull request #4746 from lucasmichot/mail-is-pretending

[4.2] Mail : add isPretending()
Merge pull request #4740 from hettiger/patch-1

Messed up Mailer (Introduced by 4.1 -> 4.2)
Fix typo.
Work on auto-restart of daemon queue workers.
Use cache repository.
Work on cache call.
Use colon.
Increment version.
Tweak how queue restarting works.