Adjust error messages

Author: ldionne

libcxx/test/libcxx/iterators/assert.next.pass.cpp

@@ -25,7 +25,7 @@ int main(int, char**) {
     forward_iterator<int *> it(a+1);
     (void)std::next(it, 1); // should work fine
     (void)std::next(it, 0); // should work fine
-    TEST_LIBCPP_ASSERT_FAILURE(std::next(it, -1), "Attempt to next(it, n) with negative n on a non-bidirectional iterator");
+    TEST_LIBCPP_ASSERT_FAILURE(std::next(it, -1), "Attempt to advance(it, n) with negative n on a non-bidirectional iterator");
 
     return 0;
 }

libcxx/test/libcxx/iterators/assert.prev.pass.cpp

@@ -31,7 +31,7 @@ int main(int, char**) {
     forward_iterator<int *> it(a+1);
     (void)std::prev(it, -1); // should work fine
     (void)std::prev(it, 0);  // should work fine
-    TEST_LIBCPP_ASSERT_FAILURE(std::prev(it, 1), "Attempt to prev(it, n) with a positive n on a non-bidirectional iterator");
+    TEST_LIBCPP_ASSERT_FAILURE(std::prev(it, 1), "Attempt to advance(it, n) with negative n on a non-bidirectional iterator");
 
     return 0;
 }