Make bench_pictures' timing more GPU friendly

This updates bench_pictures' timing methodology to more correctly reflect the GPU use case.

Ben & Eric - will this work with the performance infrastructure? It replaces the old output:

running bench [1257 3194] tabl_worldjournal.skp   simple_viewport_1500x1000_gpu: msecs =  22.22 cmsecs =  22.62

with:

running bench [1257 3194] tabl_worldjournal.skp simple_viewport_1500x1000_gpu <averaged>: msecs =  25.72 cmsecs =  24.18

Alternatively, we could just output the new timings without the "<averaged>" suffix.

[benchen, 2013-12-16 20:25:41]

Thanks Rob. If possible, please make the new outputs identical in format to the
old one, so it doesn't break the bench parser. As long as the format doesn't
change (no addition of averaged), everything should work as before. Thanks.

[robertphillips, 2013-12-16 20:31:46]

Fixed in latest patch.

[benchen, 2013-12-16 20:47:29]

On 2013/12/16 20:31:46, robertphillips wrote:
> Fixed in latest patch.

LGTM
Brian, Joe is working on JSON outputs, so please stay tuned :)

[robertphillips, 2013-12-17 13:40:38]

committed as r12705