examples: Fixed compilation errors

error: 'MULTI_PERFORM_HANG_TIMEOUT' undeclared

docs/examples/imap-multi.c

@@ -29,6 +29,8 @@
  * Note that this example requires libcurl 7.30.0 or above.
  */
 
+#define MULTI_PERFORM_HANG_TIMEOUT 60 * 1000
+
 static struct timeval tvnow(void)
 {
   struct timeval now;

docs/examples/pop3-multi.c

@@ -29,6 +29,8 @@
  * Note that this example requires libcurl 7.20.0 or above.
  */
 
+#define MULTI_PERFORM_HANG_TIMEOUT 60 * 1000
+
 static struct timeval tvnow(void)
 {
   struct timeval now;