The syntax being reverted added busywork and noise to the common case
where you want to say "I have the right address, but the wrong type,"
without adding any real safety.
Also it eliminated the ability to write UnsafePointer<T>(otherPointer),
without adding ".self" to T. Overall, it was not a win.
This reverts commits r21324 and r21342
Swift SVN r21424
Previously, it was possible to write Unsafe[Mutable]Pointer(x) and have
Swift deduce the pointee type based on context. Since reinterpreting
memory is a fundamentally type-unsafe operation, it's better to be
explicit about conversions from Unsafe[Mutable]Pointer<T> to
Unsafe[Mutable]Pointer<U>. This change is consistent with the move from
reinterpretCast(x) to unsafeBitCast(x, T.self).
Also, we've encoded the operations of explicitly adding or removing
mutability as properties, so that adding mutability can be separated
from wild reinterpretCast'ing, a much more severe form of unsafety.
Swift SVN r21324
