RFC --enable-debugging

[B. Kosnik]

>As an everyday library user, I compile and link everything with -g
>even when I build final release builds with full optimization so that
>the debugging symbols are in the binary in the event of a crash.  If
>-g becomes overloaded to also mean "pick a non-optimized library
>implementation", this could be a nasty surprise.

Yeah. This is what I think too.

I'd like to go ahead and do a proof-of-concept implementation of this,
based on just putting the debug library in prefix/lib/debug. This will
allow it to be used with -L directives.

This work has slipped to the back burner as bug-fixing for 3.2.1 has
moved into the top priority. It's first on my list of things to do when
3.2.1 ships. (Second, I guess, after merging the GLIBCPP_FORCE_NEW
work.)

-benjamin