Return 0 from int main() in the hash examples.

[SVN r30633]

examples/books.cpp

@@ -31,6 +31,8 @@ int main()
 
     //assert(books.find(knife) != books.end());
     //assert(books.find(dandelion) == books.end());
+
+    return 0;
 }
 
 namespace library

examples/point.cpp

@@ -48,5 +48,7 @@ int main()
     // hash function.
     assert(point_hasher(p1) != point_hasher(p2));
     assert(point_hasher(p1) != point_hasher(p3));
+
+    return 0;
 }
 

examples/portable.cpp

@@ -53,4 +53,6 @@ int main()
     assert(hasher(x) == hasher(x));
     assert(hasher(x) != hasher(y));
     assert(hasher(x) == hasher(z));
+
+    return 0;
 }