Log Message:
Update libsieve to 2.3.1.

libSieve 2.3.1
--------------
This release is made possible by the tremendous effort of Dilyan Palauzov.

- Many small fixes and improvements.

libSieve 2.3.0
--------------
This release is made possible by the tremendous effort of Dilyan Palauzov.

- Hide internal symbols (do not export them) from the final shared library \ 
(works with GCC>=4)

- Add support for DOT in addresses (RFC5322, 4.1. Miscellaneous Obsolete Tokens)

- libsieve is now reentrant

- Add SILENT_RULES to Makefile.am

- Move all Makefile.am-s to single /Makefile.am

- Move the build root from /src/ to /

libSieve 2.2.9
--------------

- Vacation segfault fix (thanks to Paul Stevens).

libSieve 2.2.8
--------------

- Handle empty addresses (thanks to Dilyan Palauzov).

- Short-circuit all(tests) as soon as a test fails (thanks to Dilyan Palauzov).

- Short-circuit any(tests) as soon as a test succeeds (thanks to Dilyan Palauzov).

- Check that 'myaddr' is among those specified in the script (thanks to Paul \ 
Stevens).

- Add AM_MAINTAINER_MODE to only rebuild flex/bison sources if required.