lib-sieve: Use common context for both script evaluation and action execution.

src/lib-sieve/Makefile.am

src/lib-sieve/cmd-discard.c

src/lib-sieve/cmd-redirect.c

src/lib-sieve/ext-envelope.c

src/lib-sieve/ext-reject.c

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

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

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

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

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

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

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

src/lib-sieve/plugins/mailbox/tag-mailbox-create.c

src/lib-sieve/plugins/mailbox/tst-mailboxexists.c

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

src/lib-sieve/plugins/metadata/tst-metadataexists.c

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

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

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

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