Correct return types for async function expresssions.

docs/language/dartLangSpec.tex

Index: docs/language/dartLangSpec.tex
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--- docs/language/dartLangSpec.tex	(revision 43420)
+++ docs/language/dartLangSpec.tex	(working copy)
@@ -3090,8 +3090,13 @@
 The static type of a function literal of the form 
 
 $(T_1$ $a_1, \ldots, T_n$ $a_n, [T_{n+1}$ $x_{n+1} = d_1, \ldots,  T_{n+k}$ $x_{n+k} = d_k])$ \ASYNC{} $=> e$
-is $(T_1 \ldots, T_n, [T_{n+1}$ $x_{n+1}, \ldots, T_{n+k}$ $x_{n+k}]) \rightarrow Future<T_0>$, where $T_0$ is the static type of $e$. 
+is $(T_1 \ldots, T_n, [T_{n+1}$ $x_{n+1}, \ldots, T_{n+k}$ $x_{n+k}]) \rightarrow Future<flatten(T_0)>$, where $T_0$ is the static type of $e$ and  $flatten(T) = flatten(S)$ if $T = Future<S>$, and $T$ otherwise. 
 
+\rationale{
+We collapse multiple layers of futures into one. If $e$ evaluates to a future $f$, the future will not invoke its \code{then()} callback until f completes to a non-future value, and so the result of an await is never a future, and the result of an async function will never have type \code{Future$<X>$} where $X$ itself is an invocation of \code{Future}. 
+}
+
+
 \LMHash{}
 The static type of a function literal of the form 
 
@@ -3105,7 +3110,7 @@
 
 $(T_1$ $a_1, \ldots, T_n$ $a_n, \{T_{n+1}$ $x_{n+1} : d_1, \ldots,  T_{n+k}$ $x_{n+k} : d_k\})$ \ASYNC{}  $=> e$
 
-is $(T_1 \ldots, T_n, \{T_{n+1}$ $x_{n+1}, \ldots, T_{n+k}$ $x_{n+k}\}) \rightarrow Future<T_0>$, where $T_0$ is the static type of $e$. 
+is $(T_1 \ldots, T_n, \{T_{n+1}$ $x_{n+1}, \ldots, T_{n+k}$ $x_{n+k}\}) \rightarrow Future<flatten(T_0)>$, where $T_0$ is the static type of $e$. 
 
 \LMHash{}
 The static type of a function literal of the form  
@@ -4596,14 +4601,9 @@
 }
 
 \LMHash{}
-Let $flatten(T) = flatten(S)$ if $T = Future<S>$, and $T$ otherwise. The static type of $a$ is $flatten(T)$ where $T$ is the static type of $e$.
+The static type of $a$ is $flatten(T)$ (the $flatten$ function is defined in section \ref{functionExpressions}) where $T$ is the static type of $e$.
 
-\rationale{
-We collapse multiple layers of futures into one. If $e$ evaluates to a future $f$, the future will not invoke its \code{then()} callback until f completes to a non-future value, and so the result of an await is never a future, and the result of an async function will never have type \code{Future$<X>$} where $X$ itself is an invocation of \code{Future}. 
-}
 
-
-
      
 \subsection{ Postfix Expressions}
 \LMLabel{postfixExpressions}