This change is bigger than I would have liked, so this needs to be tested more.

Before, sievec and sieve-dump would switch to mail_uid:mail_gid and then fail to compile/dump a root script.

Added test for interaction between include extension and dict script location support.

Clang static analyzer is happy now.

  - 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.

Configuration is now only read once at extension initialization.

- 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.