Fix some test warnings.

And turn on warnings as errors in Travis.

test/exception/rehash_exception_tests.cpp

@@ -18,8 +18,8 @@ struct rehash_test_base : public test::exception_base
 {
     test::random_values<T> values;
     unsigned int n;
-    rehash_test_base(unsigned int count = 100, unsigned int n = 0)
-        : values(count), n(n)
+    rehash_test_base(unsigned int count = 100, unsigned int n_ = 0)
+        : values(count), n(n_)
     {}
 
     typedef T data_type;

test/exception/swap_exception_tests.cpp

@@ -66,8 +66,8 @@ struct swap_base : public test::exception_base
     {}
 
     struct data_type {
-        data_type(T const& x, T const& y)
-            : x(x), y(y) {}
+        data_type(T const& x_, T const& y_)
+            : x(x_), y(y_) {}
 
         T x, y;
     };