swift234

Allow capturing super in explicit closures and nested functions.

The previous commit enabled this; now it's just about removing the
restriction in the parser and tightening up code completion.

Using 'super' in a closure where 'self' is captured weak or unowned still
doesn't work; the reference to 'self' within the closure is treated as
strong regardless of how it's declared. Fixing this requires a cascade of
effort, so instead I just cloned rdar://problem/19755221.

rdar://problem/14883824

Swift SVN r25065