Testsuite failures with _GLIBCXX_DEBUG

[Benjamin Kosnik]

>I spent last night looking into 10 testsuite FAILs that occur in debug
>mode, on both 3.4 and mainline. These FAILs are caused by three problems,
>two of which I've reported as libstdc++/16020 and libstdc++/16021.

10 FAILs is not so bad, but more than I remember when I did 3.4.0
release testing.

Thanks so much for doing this. I'm a bit backed up right now but will
get to this at some point.

-benjamin