Fix: case when SPOP with count>MAXINT, setTypeRandomElements() will get negative count argument due to signed/unsigned mismatch.

setTypeRandomElements() now returns unsigned long, and also uses unsigned long for anything related to count of members.
spopWithCountCommand() now uses unsigned long elements_returned instead of int, for values returned from setTypeRandomElements()
Merge pull request #2224 from advance512/spopWithCount

Fix: case when SPOP with count>MAXINT, setTypeRandomElements() will get ...