Add a failing test case around cursors and secondary reads.
Add a failing test case around cursors and secondary reads.

If we do a secondary read that is large enough to require sending a
GETMORE, and then do another query before the GETMORE, the secondary
connection gets unpinned, and the GETMORE gets sent to the wrong
server, resulting in CURSOR_NOT_FOUND, even though the cursor still
exists on the server that was initially queried.

fairplace/mongo-ruby-driver,estolfo/mongo-ruby-driver,mongodb/mongo-ruby-driver,jonhyman/mongo-ruby-driver,brandonblack/mongo-ruby-driver,kay-kim/mongo-ruby-driver,aherlihy/mongo-ruby-driver,pcarrier-packaging/deb-ruby-mongo,wandenberg/mongo-ruby-driver,namusyaka/mongo-ruby-driver,xronos-i-am/mongo-ruby-driver,saghm/mongo-ruby-driver,agis-/mongo-ruby-driver,tommyb67/mongo-ruby-driver,saghm/mongo-ruby-driver,fhwang/mongo-ruby-driver,mongodb/mongo-ruby-driver,pcarrier-packaging/deb-ruby-mongo,0x00evil/mongo-ruby-driver,pcarrier-packaging/deb-ruby-mongo,mongodb/mongo-ruby-driver,jonhyman/mongo-ruby-driver,dunedain289/mongo-ruby-driver,kay-kim/mongo-ruby-driver,AndyObtiva/mongo-ruby-driver,estolfo/mongo-ruby-driver,pcarrier-packaging/deb-ruby-mongo,pcarrier-packaging/deb-ruby-mongo,ShanaLMoore/mongo-ruby-driver