In the course of preparing the bridging object to be bridged to a Swift value, we forwarded the cast flags to _dynamicCastUnknownClass unaltered, which caused a leak for copy-on-success casts since it introduced an extra retain. Fix this by simplifying _dynamicCastUnknownClass to have no retain/release behavior of its own. Fixes rdar://problem/22587077.
Swift SVN r31841
Previously the "as" keyword could either represent coercion or or forced
downcasting. This change separates the two notions. "as" now only means
type conversion, while the new "as!" operator is used to perform forced
downcasting. If a program uses "as" where "as!" is called for, we emit a
diagnostic and fixit.
Internally, this change removes the UnresolvedCheckedCastExpr class, in
favor of directly instantiating CoerceExpr when parsing the "as"
operator, and ForcedCheckedCastExpr when parsing the "as!" operator.
Swift SVN r24253
This allows one to cast a value type (say, [String]) to AnyObject or
NSCoding, for example. It's another piece of <rdar://problem/17637959>.
Swift SVN r20964
