Testsuite: added tests on the envelope of outgoing messages produced by redirect, enotify:mailto, reject and vacation.

Major rework of envelope address handling: a normalized version of the envelope addresses is maintained in the message context and message context is now also available during action execution.

Imap4flags: added support for obsolete imapflags extension for backwards compatibility with CMUSieve.

Removed code duplication between testsuite and commandline tools. Also restructured source code of the tools.

Added the concept of a script code header to list the extensions actually used by a script (was using all extensions listed in the binary).

Significantly improved handling of old/corrupt binaries and revised matching implementation in the process.

Fixed code emission for extension-defined variables and removed hardcoded paths from include extension.