mail: add strict (#825)

* mail: add strict

* The message about "strict" in the BUGS section of the manual was a reminder to make this change
* Do mechanically with set/get functions what was being done with AUTOLOAD
* Attribute "status" in object "message" was never used
* Attribute "append" in object "mailbox" was never used
* Many local variables were not declared before use
* Bump version

* strict had allowed list-deref of undef in replyCC()