Changed id_code for optional operands to signed and fixed a ext_my_id-related error in the vacation and copy extensions.

Removed part of the code duplication between address-part, match-type and comparator implementations.

Added support for externally adding tags to (possibly not yet registered) command. The copy extension now adds such a tag to fileinto and redirect.

Almost finished implementing the store action. But, I still get strange errors when the mail transaction commits. Mail is stored though.

Moved address-part, match-type and comparator code registries from interpreter to binary where they belong.