Before, it would only terminate the test when it failed explicitly using the
test_fail command.

Found with clang -Wstrict-bool.

Fixed a few printf format problems in the process.
Updated test suite to account for the new number width.

Clang static analyzer is happy now.

lib-sieve: optimized compilation of tests that yield constant results (i.e. known at compile tme), such as true and false.
If the result of a test is known at compile time, it is optimized away. If an if-command depends on an entirely constant test, it is optimized away as well,
causing only the 'true' sub-block to be compiled.

Fixed various compile warnings related to spurious semicolons and inappropriate variable initialization.

- 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.

Testsuite: added support for testing delivered messages by looping these back as the evaluated message. Added tests for the fileinto command.