Adapt to effective types checks for pointer vars

Fixes two cases where the tutorial was not compliant with
VeriFast's new checks for compliance with C's effective types
rules when accessing variables of pointer type (see
verifast/verifast#542).

tutorial.tex

@@ -1756,7 +1756,7 @@ \section{By-Reference Parameters}\label{section:byref-params}
 second argument is the current value of the variable.
 
 It follows that the following is a valid contract for function
-\lstinline!nodes_filter!:
+\lstinline!nodes_filter!:\footnote{This sentence is \emph{almost} true. This is a valid contract for function \lstinline!nodes_filter! only if C's \emph{effective types} rules are disabled, by specifying \lstinline|-fno-strict-aliasing| on the C compiler's and VeriFast's command line, or by checking \emph{Assume untyped memory} in the VeriFast IDE's Verify menu. To verify compliance with C's effective types rules when accessing the variable pointed to by \lstinline|n| as a variable of type \lstinline|struct node *|, VeriFast checks that that is that variable's \emph{effective type}, expressed in VeriFast syntax as \lstinline|has_type(node, &typeid(struct node *)) == true|. You can ignore this complexity by using the points-to syntax \lstinline!*n |-> ?node!, which implies both the \lstinline|pointer| chunk and the \lstinline|has_type| fact.}
 \begin{lstlisting}
 void nodes_filter(struct node **n, int_predicate *p)
     //@ requires pointer(n, ?node) &*& nodes(node, _) &*& is_int_predicate(p) == true;
@@ -4254,7 +4254,7 @@ \section{Arrays of Pointers}\label{section:arrays-of-pointers}
     printf("How many students do you have? ");
     int n = read_int();
     if (n < 0 || 0x20000000 <= n) abort();
-    char **names = malloc(n * sizeof(char **));
+    char **names = malloc(n * sizeof(char *));
     if (names == 0) abort();
     for (int i = 0; i != n; i++) {
         printf("Please enter the name of student number %d: ", i + 1);