0.12dev: Added the possibility to send e-mail through a `sendmail`-compatible executable instead of SMTP.
0.12dev: Added the possibility to send e-mail through a `sendmail`-compatible executable instead of SMTP.

 * Abstracted e-mail sending into an interface `IEmailSender`.
 * Transformed the existing SMTP implementation into `SmtpEmailSender`.
 * Added `SendmailEmailSender`.

Closes #3870.


git-svn-id: eda3d06fcef731589ace1b284159cead3416df9b@7935 af82e41b-90c4-0310-8c96-b1721e28e2e2

walty8/trac,walty8/trac,netjunki/trac-Pygit2,netjunki/trac-Pygit2,walty8/trac,jun66j5/trac-ja,walty8/trac,jun66j5/trac-ja,jun66j5/trac-ja,jun66j5/trac-ja,netjunki/trac-Pygit2