tests; add authSource test
fixed; multiple bg index creation

In MongoDB < 2.4, multiple background indexes creation is not
well supported. We now create indexes one-by-one.

closes #1365
test; added for #1365

#1365
fixed; pull / set subdoc combination

closes #1303
test; added for saveable required populated buffers
backport fix for saving required populated buffers
release 3.5.9