RFC --enable-debugging

[Benjamin Kosnik]

>I think this is confusing.  
>
>If we were to specify an alternate directory, I would prefer
>
>   -enable-debug-dir=

We're trying to re-use some of the --enable-debug bits. I think it makes
most sense the way Phil proposed it, as --enable-debug=foo, with a
default being (prefix)/lib/debug. Many of the other --enable-xxx flags
have arguments that specify non-default behavior (--enable-cheaders,
--enable-clocale, etc.)

-benjamin