Disallow array_ptrs to function types. (checkedc#204)

Update the specification to disallow array_ptrs of function types. Bounds checking pointers to function types does not make sense because functions do not have sizes in C.  This addiresses issue checkedc#34.

Also correct the capitalization of the _Nt_array_ptr keyword in the specification.

Author: dtarditi

spec/bounds_safety/core-extensions.tex

@@ -22,7 +22,7 @@ \section{New keywords}
 begin with two underscores \cite[Section 7.1.3]{ISO2011}. The following
 new keywords are introduced:
 \begin{verbatim}
-_Array_ptr  _Checked  _Dynamic_check  _Nt_Array_ptr  _Nt_checked  _Ptr
+_Array_ptr  _Checked  _Dynamic_check  _Nt_array_ptr  _Nt_checked  _Ptr
 _Where  _Unchecked
 \end{verbatim}
 
@@ -140,6 +140,15 @@ \section{New kinds of pointer types}
 \keyword{const} value can be assigned a pointer to a non-const value.  
 The reverse is not allowed.
 
+Array pointers (\arrayptr) of function types are not allowed. Functions have
+no size associated with them, so bounds checking pointers to them does not
+make sense.  Programmers should use \ptr\ instead:
+\begin{verbatim}
+typedef array_ptr<int (int x, int y)> callback_fn; // illegal
+typedef ptr<int (int x, int y)> callback_ptr;      // legal
+typedef array_ptr<callback_ptr> callback_arr;      // legal
+\end{verbatim}
+
 \section{New kinds of array types}
 
 A new checked array type is added to C. Just as there are checked pointer