This change allows a Nexter to be used in the same manner as a scanner
using a for graph.Next(it) {} construction.
It is important that graph.Next(it) and any associated it.Result() calls
operate on the same iterator.
This is done unsubtlely at the moment and there is plenty of room for
optimisation of assertion location to prevent repeated reasserting as is
done now.
These packages really impact on test readability with crazy action at a
distance. In addition to this removal of goconvey reduced the test run
time for leveldb on average by about 40-50%.
