SAVEDATE work out behaviour when unsupported by the implementation

[brong]

Currently the text says [FIXME: This is what Dovecot currently does, but for a
standard this is inappropriate. It should probably indicate the lack
of support with a particular NO response code, or it could just
return NULL or some other special value].

This needs to be resolved before publication.

It is also necessary to document how the SEARCH extensions work

[stephanbosch]

See the discussions on the mailing list. I am still not sure how to address this.

[stephanbosch]

Addressed in latest draft.