Most tests were using %swift or similar substitutions, which did not
include the target triple and SDK. The driver was defaulting to the
host OS. Thus, we could not run the tests when the standard library was
not built for OS X.
Swift SVN r24504
Previously, it had a *nearly* pre-order traversal, but included private
imports before the top-level module being searched. This was leading to
strange errors that relied on search order, like
<rdar://problem/17127940> Qualifying Swift types by their module name doesn't work
Swift SVN r18806
This is the Swift equivalent of allowing Cocoa.NSWindow to find
AppKit.NSWindow (or AppKit.NSWindow.NSWindow, really). Some of these
error messages could be improved, but the basic semantics are correct.
Swift SVN r6855
