[Patch] Move pback members from basic_streambuf to basic_filebuf

[Andreas Tobler]

Hi Paolo,

Paolo Carlini wrote:
> Andreas Tobler wrote:
> 
>> I'll have a short break and test when I'm back.
> 
> 
> Ok, this time is for real ;-)
> 
> Please Andreas test the below. Thanks!

Hope I did it right! (as said 27_io)

Running 
/Volumes/xufs/gcc-cvs/gcc/libstdc++-v3/testsuite/libstdc++-v3.dg/dg.exp ...
FAIL: 27_io/basic_filebuf/open/char/9507.cc execution test
/Volumes/xufs/gcc-cvs/gcc/libstdc++-v3/testsuite/27_io/basic_filebuf/open/char/9
507.cc:56: failed assertion `!fbuf.is_open()'

                 === libstdc++-v3 Summary ===

# of expected passes            532
# of unexpected failures        1

 From my side ok to ci.

Thanks!

& Regards, good night!

Andreas