Adjusted tag parameter validation API.

src/lib-sieve/plugins/body/tst-body.c

src/lib-sieve/plugins/date/tst-date.c

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

src/lib-sieve/plugins/imap4flags/tag-flags.c

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

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

src/lib-sieve/sieve-validator.c

src/lib-sieve/sieve-validator.h

src/testsuite/cmd-test-message.c

src/testsuite/tst-test-error.c

src/testsuite/tst-test-result.c