Testsuite: extended multiscript testing.

src/lib-sieve/sieve-actions.c

src/lib-sieve/sieve-result.c

src/lib-sieve/sieve-result.h

src/lib-sieve/sieve.c

src/testsuite/testsuite-result.c

tests/multiscript/conflicts.svtest

tests/multiscript/fileinto-frop.sieve

tests/multiscript/keep.sieve