binding benchmarks (experimental, see #590)

[paolopas]

Use with legacy.jam (e.g. b2 -flegacy.jam)

NATIVE_RULE benchmark : timed ;
IMPORT benchmark : timed : : benchmark.timed ;
while true { benchmark.timed qwerty ; }

or with Jamroot

import benchmark ;
while true { benchmark.timed qwerty ; }

see #590