fix to continue function

[arthurprevot]

Ran into an issue when loading the next batch of 2500 records from a SOAP API retrieve operation. The first batch was fine but the 2nd one, i.e. the first one using the continue method, was not, sending back a message with a status labelled as Error. The problem was documented in http://salesforce.stackexchange.com/questions/24911/error-on-making-continue-request-while-retrieving-all-subscribers-from-a-list. This PR implements that fix since it solved the issue for me as well.

[ses4j]

Pulled this in to fix FuelSDK::Subscriber, now getResults.continue "works". However, it seems to append the new results to the old results, so:

results = subscriber.continue
results.length == 5000 after page 2...
results.length == 7500 after page 3...

[Gokul595]

It fixes the issue in continue method.

[Ksm125]

we should also have in the unpack method

@results = (unpack_rslts raw)

instead of

@results += (unpack_rslts raw)

to not overflow the memory