Cleaned up commands implementation.

src/lib-sieve/Makefile.am

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/cmd-require.c

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

src/lib-sieve/plugins/include/cmd-import.c

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

src/lib-sieve/sieve-actions.h

src/lib-sieve/sieve-code-dumper.c

src/lib-sieve/sieve-commands-private.h

src/lib-sieve/sieve-commands.c

src/lib-sieve/sieve-commands.h

src/lib-sieve/sieve-generator.c

src/lib-sieve/sieve-interpreter.c

src/lib-sieve/sieve-validator.c

src/lib-sieve/tst-address.c

src/lib-sieve/tst-allof.c

src/lib-sieve/tst-anyof.c