Major changes in the extensions support.

src/lib-sieve/cmd-discard.c

src/lib-sieve/cmd-if.c

src/lib-sieve/cmd-keep.c

src/lib-sieve/cmd-redirect.c

src/lib-sieve/ext-encoded-character.c

src/lib-sieve/ext-envelope.c

src/lib-sieve/ext-fileinto.c

src/lib-sieve/ext-reject.c

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

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

...gins/comparator-i-ascii-numeric/ext-cmp-i-ascii-numeric.c

src/lib-sieve/plugins/copy/copy.sieve

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

src/lib-sieve/plugins/imapflags/cmd-addflag.c

src/lib-sieve/plugins/imapflags/cmd-removeflag.c

src/lib-sieve/plugins/imapflags/cmd-setflag.c

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

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

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

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