Final patch for libstdc++ _M_open_mode and related

[gdr@cs.tamu.edu]

Quoting Zack Weinberg <zack@codesourcery.com>:

> 
> The only change from the previous revision of this patch is, I put
> back a typo fix in the test cases that was in the original but got
> dropped out by mistake in the first revision.  Oh, and as requested
> the baseline-symbols.txt changes are dropped from the 3.4 patch.
> ChangeLogs remain the same, mostly.
> 
> Bootstrapped i686-linux, applied 3.4 and mainline.  Gaby, OK for 3.3
> branch?

Yes