[v3] debug mode

[Benjamin Kosnik]

This patch comes in two parts. 

g++
http://people.redhat.com/bkoz/namespace_association.patch

libstdc++
http://people.redhat.com/bkoz/libstdc++_debug_mode.patch

This is work that was started in June with this message:
http://gcc.gnu.org/ml/libstdc++/2003-06/msg00099.html

Iterative work happened throughout the summer
http://gcc.gnu.org/ml/libstdc++/2003-07/msg00255.html
http://gcc.gnu.org/ml/libstdc++/2003-07/msg00372.html
http://gcc.gnu.org/ml/libstdc++/2003-08/msg00177.html

At the end of August, Jason, Gaby and I started working on an
alternate approach for the linkage issue, using namespace
syntax. Details can be found in the Pre-Kona mailing for the C++
standards body, in document n1526.

By the end of this meeting, we had reached a consensus on the approach
and now have an implementation that all parties feels is correct. Many
thanks to Jason, Gaby, Matt, Doug, Mark etc. etc.  who have contributed
or reviewed versions of this work.

This patch has been tested on x86/linux, in debug and non-debug
modes. There are no additional failures for either mode. In addition,
third party testsuites have been run to verify no unanticipated ABI
impacts. Testsuite logs for the non-proprietary testsuite runs are
available on request.

Although this patch is late, one vendor (Apple) is already shipping a
released compiler with a previous version of this patch and another
vendor (Red Hat, probably others) has received customer demands for
this functionality. It behooves the gcc community to get a version of
this functionality in the next major FSF release that all the
principal parties can use. The size of the runtime patch makes keeping
this as a vendor branch impractical, and the thought of continued
maintenance of this approach is horrific...

In addition, since 3.4 is scheduled for an ABI bump for C++, it is
imperative that this patch be accepted, as it changes the mangling on
some STL containers to support the debug mode.

This has been approved off-list for 3.4 by Mark:

> Given the C++ ABI impact, and the fact that you've tested 
> this patch very extensively, this patch is OK for 3.4.

best,
benjamin