Revised extension support for match-types.

TODO

src/lib-sieve/cmp-i-octet.c

src/lib-sieve/mcht-contains.c

src/lib-sieve/mcht-is.c

src/lib-sieve/mcht-matches.c

src/lib-sieve/plugins/regex/Makefile.am

src/lib-sieve/plugins/regex/ext-regex-common.c

src/lib-sieve/plugins/regex/ext-regex-common.h

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

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

src/lib-sieve/plugins/relational/ext-relational-common.c

src/lib-sieve/plugins/relational/ext-relational-common.h

src/lib-sieve/plugins/relational/ext-relational.c

src/lib-sieve/plugins/relational/mcht-count.c

src/lib-sieve/plugins/relational/mcht-value.c

src/lib-sieve/sieve-comparators.c

src/lib-sieve/sieve-comparators.h

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

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