bug#3465: 23.0.94; feature request: be able to log minibuffer messages

Feature request: Be able to log minibuffer messages, that is, messages
from `minibuffer-message'.
 
For example, option `message-log-max', which allows for disabling
logging, could have additional values:
 
* negative N means (abs N) max lines + log minibuf msgs too
* other non-nil value, besides t and N, means log minibuf msgs too
 
With minibuffer messages logged also, a user can consult *Messages*
(e.g. using `C-x C-b') if s?he misses an ephemeral message.

In GNU Emacs 23.0.94.1 (i386-mingw-nt5.1.2600)
 of 2009-05-24 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4)'