Comprehensive spelling/typo fixes.

Thanks to Josh Soref for generating these fixes.

src/log.c

@@ -154,7 +154,7 @@ static void log_write(void)
    
   while (entries)
     {
-      /* The data in the payoad is written with a terminating zero character 
+      /* The data in the payload is written with a terminating zero character 
 	 and the length reflects this. For a stream connection we need to 
 	 send the zero as a record terminator, but this isn't done for a 
 	 datagram connection, so treat the length as one less than reality 
@@ -436,7 +436,7 @@ void check_log_writer(int force)
 void flush_log(void)
 {
   /* write until queue empty, but don't loop forever if there's
-   no connection to the syslog in existance */
+   no connection to the syslog in existence */
   while (log_fd != -1)
     {
       struct timespec waiter;