Updated binary version.

Doveadm-sieve plugin may be broken at this point; not tested so far.

Those version numbers are now also stored in the binary, making sure it is recompiled
when a new version of an extension is used. This avoids updating the binary version
for minor changes to extensions and also makes this work for plugins.

  - Built generic interface for alternative script sources.
  - Implemented dict script location.
  NOTE: ManageSieve will not work with this yet, nor will sieve_before/sieve_after.

- Added sieve_global_extensions setting.

Vacation extension: added min/max period configuration settings and changed the internal unit from days to seconds.

- 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.

Made sure that scripts are only recompiled when the script file - or the symlink pointing to it - is strictly newer.

Be explicit about signedness of data in binary code representation. Some architectures, like ARM, differ in this respect.

Enabled (optional) support for Valgrind in the testsuite and fixed a few intricate bugs in the process.

Properly implemented dumping a binary including a list of required extensions and support for extension-specific output.

RECOVERED FROM INCONSISTENCY: developed testsuite and binary dumping and fixed various small issues.

Basic include functionality seems to be working and if source scripts are changed the binary is always recompiled.