Implement journaling. Bug #17240.

* msg-ui.c (handle_msg): Send message to write_journal function
as well as msg_file.
(dump_message): Change interface so that it takes a function
pointer instead of a FILE.
(write_stream): New function.
(write_journal): New function.

* read-line.c (welcome): Call journal_enable, so that the journal
is enabled by default.

* automake.mk (output_sources): Add journal.c, journal.h.

* journal.c: New file.

* journal.h: New file.