Circular iteration on tuple starting from a specific index

[guillaume.paulet at giome.fr]

@Gregory Ewing: you were right, your version without *chain* is faster 
and I quiet like it :)

```
from timeit import timeit
from itertools import chain, cycle, islice

def cycle_once_with_chain(sequence, start):
      return chain(islice(sequence, start, None), islice(sequence, 
start))


def cycle_once_without_chain(sequence, start):
      return islice(cycle(sequence), start, start + len(sequence))


sequence = tuple(i for i in range(100))

time_with_chain = timeit(
     stmt='cycle_once_with_chain(sequence, 50)',
     number=1000000, globals=globals()
)
print('Method with *chain* took: ', (time_with_chain /1000000), ' per 
call.')
# Method with *chain* took:  5.025957580000977e-07  per call.

time_without_chain = timeit(
     stmt='cycle_once_without_chain(sequence, 50)',
     number=1000000, globals=globals()
)
print('Method without *chain* took: ', (time_without_chain /1000000), ' 
per call.')
#Method without *chain* took:  3.5880194699984714e-07  per call.
```

@Ian: Good point here, these two methods only works with sequences 
(list, tuple, string...).

I renamed it appropriately in the above sample code :)