Add a 'mayTakeValue' function, which returns true if we're allowed to take the value from an existential container (assuming we own the existential container value). This is true for class and opaque existential containers, but not for boxed existentials, where multiple owners may share references to the boxed value. Also add a 'deinitExistentialContainer' function to do any cleanup that must happen after the value has been consumed out of an existential container. Fix up an off-by-one indirection level in the SwiftError implementations of the existing existential container methods.
Swift SVN r26561
Teach ExistentialTypeMetadata how to project out the value pointer, type metadata, and protocol witness table from ErrorType containers. NFC yet; the dynamic casting and reflection machinery needs further work to correctly handle ErrorType boxes.
Swift SVN r26509
If an existential type for a special protocol (not a composition) is instantiated, carry the special protocol identifier from that protocol to the existential, allowing us to easily recognize existentials with unique runtime characteristics.
Swift SVN r26436
The standard library has grown significantly, and we need a new
directory structure that clearly reflects the role of the APIs, and
allows future growth.
See stdlib/{public,internal,private}/README.txt for more information.
Swift SVN r25876
