Upon upload, the include extension is more lenient towards circular includes and missing scripts as required by RFC.
The script is now also verified upon SETACTIVE when it was not active before.
However, this new SETACTIVE behavior is not optimal for the situation where the active script was updated with
PUTSCRIPT and contains an nonexistent include (ignored during upload). This can still cause runtime errors, since
an already active script is not verified again during SETACTIVE.

- Now compiles regularly without --with-unfinished-features
- Still experimental though, so be careful.
- Changed command structure a bit, removing the useless -M option.

- Updated documentation.
- Made editheader extension disabled by default

lib-sieve: optimized compilation of tests that yield constant results (i.e. known at compile tme), such as true and false.
If the result of a test is known at compile time, it is optimized away. If an if-command depends on an entirely constant test, it is optimized away as well,
causing only the 'true' sub-block to be compiled.

ManageSieve: removed TODO status of adding ANONYMOUS SASL support, since the RFC specification no longer describes it.

Enforced ManageSieve protocol syntax better with some of the commands; some commands still allowed spurious extra arguments.

- Changed operand read functions to prove exec status return codes in stead of boolean.
- Restructured optional-operand, stringlist and string-match APIs to provide execution status (error code) upon failure.
- Corruption errors are only produced when the binary is actually corrupt. Normal failures should never cause a recompile attempt anymore.
- Simplified optional-operand API.
- Cleaned up test command implementations that use the string-match API.

- Administrators now get properly notified about uncompiled global scripts and the inability of the sieve plugin to store global binaries.
- Improved binary load/save error handling and fixed a few smal bugs.
- Simplified ManageSieve error handling.