Fixed Sieve script name checking to properly handle length issues and added 0x00ff as invalid character.

- 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.

Fixed bug in the derivation of the binary path from the script path. A bare filename would yield a path relative to root.

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

Reversed stat() and open() on two occasions to make retrieved stat information guaranteed to be valid for the opened file and added error handling for various close() system calls.

Made error reporting cleaner by avoiding the scriptname of the main script and indicating that the printed numbers are in fact source code lines.