Optimize hashtable allocator

[Jonathan Wakely]

On 2 November 2012 02:58, Paolo Carlini wrote:
> On 11/02/2012 02:48 AM, Jonathan Wakely wrote:
>>
>> This fixes the hashtable and forward_list printers.
>
> Thanks: testsuite clean again for me!

As Francois pointed out, the printers for tr1 hash tables don't work
any more, and I'm still seeing PR 55041 and confused by it (and also
confused by F16's gdb being unusable with GCC trunk).  Either I'm
being dumb and failing to see something or we need Tom to help out
with 55041.