Multiscript: improved handling of the keep action.

src/lib-sieve/cmd-redirect.c

src/lib-sieve/ext-reject.c

src/lib-sieve/plugins/enotify/cmd-notify.c

src/lib-sieve/plugins/vacation/cmd-vacation.c

src/lib-sieve/sieve-actions.c

src/lib-sieve/sieve-actions.h

src/lib-sieve/sieve-result.c

src/lib-sieve/sieve-result.h

src/lib-sieve/sieve.c

src/lib-sieve/sieve.h

src/sieve-tools/sieve-test.c