In C++0x mode, import iota and is_sorted from namespace std into

In C++0x mode, import iota and is_sorted from namespace std into
namespace __gnu_cxx to avoid ambiguous call errors.  copy_n would be a
good candidate for this too, except it was standardized with a
different return type.

Tested:
  `make -k check-c++` on x86_64-unknown-linux-gnu.

libstdc++-v3/ChangeLog:

2011-04-06  Jeffrey Yasskin  <jyasskin@google.com>

        * include/ext/algorithm (is_sorted): In C++0x mode import from
        namespace std.
        * include/ext/numeric (iota): In C++0x mode import from
        namespace std.
        * testsuite/ext/is_sorted/cxx0x.cc: New.
        * testsuite/ext/iota/cxx0x.cc: New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@172073 138bc75d-0d04-0410-961f-82ee72b054a4