Dropdown should allow "hidden search" capability

[tomsmalley]

When a select element is focused, an option can be selected by typing in the text of the desired element. I've seen two behaviours: single letter search, where only the last entry is counted; and full entry search, where the entire entry is used and the user can even to make corrections.

This should share functionality with the true search enabled dropdowns, which have the latter behaviour but in a real text box, and the items are filtered.