Cleaned up match type implementation.

src/lib-sieve/ext-envelope.c

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

src/lib-sieve/plugins/imapflags/tst-hasflag.c

src/lib-sieve/plugins/regex/mcht-regex.c

src/lib-sieve/plugins/variables/tst-string.c

src/lib-sieve/sieve-comparators.h

src/lib-sieve/sieve-match-types.c

src/lib-sieve/sieve-match-types.h

src/lib-sieve/tst-address.c

src/lib-sieve/tst-header.c

src/testsuite/tst-test-error.c

tests/compile/errors.svtest

tests/compile/errors/match-type.sieve