Doc for compdef and #compdef is out of date

["Bart Schaefer" <schaefer@xxxxxxxxxxxxxxxx>]

There's no mention of `#compdef -T ...' or of what that translates into
in the actual `compdef' command; there's also no mention of using a comma-
separated list of context names [as is described under the entry for the
`_complete' function].

I'd take a stab at documenting this, but it'd be better if somebody who
really knows what's going on there (Oliver?) would do it instead.

Also, there's an extraneous newline in the item(tt(#compdef) ...) line
which is causing the hanging tag on the paragraph to wrap incorrectly.