[kernel] Fix mailbox bugs

This commit contains a number of related mailbox issues:

- Add extra parameters to mailbox_respond_receive to allow both the
  number of bytes/handles passed in, and the size of the byte/handle
  buffers to be passed in.
- Don't delete mailbox messages on receipt if the caller is waiting on
  reply
- Correctly pass status messages along with a mailbox::replyer object
- Actually wake the calling thread in the mailbox::replyer dtor
- Make sure to release locks _before_ calling thread::wake() on blocked
  threads, as that may cause them to be scheduled ahead of the current
  thread.

definitions/objects/mailbox.def

@@ -55,9 +55,11 @@ object mailbox : object {
     method respond_receive [cap:receive] {
         param tag uint64 [inout]
         param data buffer [inout zero_ok]
+        param data_in size
         param handles ref object [inout list zero_ok]
+        param handles_in size
         param reply_tag uint16 [inout]
-        param badge uint64 [out]
+        param badge uint64 [out optional]
         param flags uint64
     }
 }