Bump I/O buffer size to 64K. We don't use PIPE_BUF or _PC_PIPE_BUF

for this because that corresponds to the value for atomic pipe
writes.  The actual pipe buffer is much larger on modern systems
and 64K is what BSD and Linux support for large pipe buffers.

src/exec_pty.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2009-2015 Todd C. Miller <Todd.Miller@courtesan.com>
+ * Copyright (c) 2009-2016 Todd C. Miller <Todd.Miller@courtesan.com>
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -78,7 +78,7 @@ struct io_buffer {
     sudo_io_action_t action;
     int len; /* buffer length (how much produced) */
     int off; /* write position (how much already consumed) */
-    char buf[32 * 1024];
+    char buf[64 * 1024];
 };
 SLIST_HEAD(io_buffer_list, io_buffer);