Old name is now deprecated.
Support for the even older global_script_path name for this setting is dropped.

Setting sieve_max_redirects=0 now means that redirects are prohibited rather than unlimited.
Now there is always a limit, but it can be enormous if the administrator wants to.

- Added sieve_global_extensions setting.

- Updated documentation.
- Made editheader extension disabled by default

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