Added editheader support.

Makefile.am

README

TODO

configure.in

doc/rfc/editheader.rfc5293.txt

src/lib-sieve/Makefile.am

src/lib-sieve/cmd-keep.c

src/lib-sieve/cmd-redirect.c

src/lib-sieve/edit-mail.c

src/lib-sieve/edit-mail.h

src/lib-sieve/ext-fileinto.c

src/lib-sieve/plugins/Makefile.am

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

src/lib-sieve/plugins/editheader/cmd-addheader.c

src/lib-sieve/plugins/editheader/cmd-deleteheader.c

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

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

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

src/lib-sieve/rfc2822.c

src/lib-sieve/rfc2822.h