[patch] Two small libstdc++ testsuite tweaks

[Jonathan Wakely]

For the custom pointer type in testsuite_allocator.h to satisfy the
RandomAccessIterator requirements it needs operator[], so this adds
it.

I'm not sure what 21_strings/basic_string/operators/char/1.cc was
testing originally, but we might as well verify the string contents
that the comments say we should get.

Tested powerpc64-linux, committed to trunk.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: patch.txt
Type: text/x-patch
Size: 1705 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/libstdc++/attachments/20150910/f93c86a6/attachment.bin>