Fix some even-more-verbose GCC warnings in the examples

Ref4_event.txt

@@ -96,9 +96,9 @@ void main_loop(evutil_socket_t fd1, evutil_socket_t fd2)
  nonblocking. */
 
  ev1 = event_new(base, fd1, EV_TIMEOUT|EV_READ|EV_PERSIST, cb_func,
- "Reading event");
+ (char*)"Reading event");
  ev2 = event_new(base, fd2, EV_WRITE|EV_PERSIST, cb_func,
- "Writing event");
+ (char*)"Writing event");
 
  event_add(ev1, &five_seconds);
  event_add(ev2, NULL);

Ref7_evbuffer.txt

@@ -666,26 +666,30 @@ if (evbuffer_commit_space(buf, v, i) < 0)
  DO NOT IMITATE THIS CODE. */
 struct evbuffer_iovec v[2];
 
-/* Do not use the pointers from evbuffer_reserve_space() after
- calling any functions that modify the buffer. */
-evbuffer_reserve_space(buf, 1024, v, 2);
-evbuffer_add(buf, "X", 1);
-/* WRONG: This next line won't work if evbuffer_add needed to rearrange
- the buffer's contents. It might even crash your program. Instead,
- you add the data before calling evbuffer_reserve_space. */
-memset(v[0].iov_base, 'Y', v[0].iov_len-1);
-evbuffer_commit_space(buf, v, 1);
-
-/* Do not modify the iov_base pointers. */
-char *data = "Here is some data";
-evbuffer_reserve_space(buf, strlen(data), v, 1);
-/* WRONG: The next line will not do what you want. Instead, you
- should _copy_ the contents of data into v[0].iov_base. */
-v[0].iov_base = data;
-v[0].iov_len = strlen(data);
-/* In this case, evbuffer_commit_space might give an error if you're
- lucky */
-evbuffer_commit_space(buf, v, 1);
+{
+ /* Do not use the pointers from evbuffer_reserve_space() after
+ calling any functions that modify the buffer. */
+ evbuffer_reserve_space(buf, 1024, v, 2);
+ evbuffer_add(buf, "X", 1);
+ /* WRONG: This next line won't work if evbuffer_add needed to rearrange
+ the buffer's contents. It might even crash your program. Instead,
+ you add the data before calling evbuffer_reserve_space. */
+ memset(v[0].iov_base, 'Y', v[0].iov_len-1);
+ evbuffer_commit_space(buf, v, 1);
+}
+
+{
+ /* Do not modify the iov_base pointers. */
+ const char *data = "Here is some data";
+ evbuffer_reserve_space(buf, strlen(data), v, 1);
+ /* WRONG: The next line will not do what you want. Instead, you
+ should _copy_ the contents of data into v[0].iov_base. */
+ v[0].iov_base = (char*) data;
+ v[0].iov_len = strlen(data);
+ /* In this case, evbuffer_commit_space might give an error if you're
+ lucky */
+ evbuffer_commit_space(buf, v, 1);
+}
 --------
 
 These functions have existed with their present interfaces since Libevent