Merge pull request swiftlang#210 from ktopley-apple/dispatch-time-0-doc

Adding documentation to clarify the result of DispatchTime(uptimeNanoseconds: 0)

Signed-off-by: Daniel A. Steffen <[email protected]>

Author: moiseev

PATCHES

@@ -309,3 +309,4 @@ github commits starting with 29bdc2f from
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+[787dd92] APPLIED rdar://30568673