ManageSieve: fixed dump-capability problem occuring when using a custom config file (patch by Timo Sirainen).

Sieve plugin: only refer to user log for compile error details when there is actually a compile error.

Fixed default Sieve capability: extra extensions spamtest, spamtestplus and virustest were also enabled by default.

ManageSieve: settings plugin, capability dump: argument array for execv was too short by one element.

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

Enforced ManageSieve protocol syntax better with some of the commands; some commands still allowed spurious extra arguments.

- Changed operand read functions to prove exec status return codes in stead of boolean.
- Restructured optional-operand, stringlist and string-match APIs to provide execution status (error code) upon failure.
- Corruption errors are only produced when the binary is actually corrupt. Normal failures should never cause a recompile attempt anymore.
- Simplified optional-operand API.
- Cleaned up test command implementations that use the string-match API.

Produce a nicer error message when trying to load with non-lda/lmtp binary (patch by Timo Sirainen).

- 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.

ManageSieve/Sieve storag: fixed error handling of PUTSCRIPT commmand; save commit errors would not make the command fail.