Provide explicit parameter type

Provide explicit parameter type when looking for snippet methods
Set Date header when sending mail

(apparently some spam filters want to see it to stay happy)
Share init key value

Previously an effectively independent value was used for each *Var
backing store.  Depending on the situation this can result in large
amounts of wasted memory (particularly with ScreenVars).
Include option attributes in multiSelect_*
Merge pull request #1595 from lift/pmb_lift_26_pending

Pending 2.6 changes (pbrant)