rethinkdb export now limits the number of processes to 1 + 2*clients
rethinkdb export now limits the number of processes to 1 + 2*clients

Fixes #4809

mbroadst/rethinkdb,niieani/rethinkdb,bchavez/rethinkdb,Qinusty/rethinkdb,jmptrader/rethinkdb,catroot/rethinkdb,mbroadst/rethinkdb,grandquista/rethinkdb,bpradipt/rethinkdb,bchavez/rethinkdb,eliangidoni/rethinkdb,grandquista/rethinkdb,niieani/rethinkdb,dparnell/rethinkdb,grandquista/rethinkdb,bchavez/rethinkdb,JackieXie168/rethinkdb,robertjpayne/rethinkdb,JackieXie168/rethinkdb,catroot/rethinkdb,bchavez/rethinkdb,jmptrader/rethinkdb,dparnell/rethinkdb,catroot/rethinkdb,robertjpayne/rethinkdb,eliangidoni/rethinkdb,dparnell/rethinkdb,dparnell/rethinkdb,Qinusty/rethinkdb,catroot/rethinkdb,Qinusty/rethinkdb,dparnell/rethinkdb,eliangidoni/rethinkdb,Qinusty/rethinkdb,jmptrader/rethinkdb,bchavez/rethinkdb,robertjpayne/rethinkdb,bchavez/rethinkdb,grandquista/rethinkdb,eliangidoni/rethinkdb,robertjpayne/rethinkdb,bpradipt/rethinkdb,bpradipt/rethinkdb,niieani/rethinkdb,JackieXie168/rethinkdb,JackieXie168/rethinkdb,Qinusty/rethinkdb,eliangidoni/rethinkdb,grandquista/rethinkdb,mbroadst/rethinkdb,mbroadst/rethinkdb,jmptrader/rethinkdb,catroot/rethinkdb,niieani/rethinkdb,bpradipt/rethinkdb,Qinusty/rethinkdb,eliangidoni/rethinkdb,JackieXie168/rethinkdb,bpradipt/rethinkdb,robertjpayne/rethinkdb,mbroadst/rethinkdb,bpradipt/rethinkdb,dparnell/rethinkdb,robertjpayne/rethinkdb,catroot/rethinkdb,JackieXie168/rethinkdb,dparnell/rethinkdb,bchavez/rethinkdb,mbroadst/rethinkdb,mbroadst/rethinkdb,robertjpayne/rethinkdb,dparnell/rethinkdb,catroot/rethinkdb,eliangidoni/rethinkdb,bchavez/rethinkdb,niieani/rethinkdb,niieani/rethinkdb,Qinusty/rethinkdb,jmptrader/rethinkdb,jmptrader/rethinkdb,catroot/rethinkdb,Qinusty/rethinkdb,robertjpayne/rethinkdb,bpradipt/rethinkdb,bchavez/rethinkdb,mbroadst/rethinkdb,grandquista/rethinkdb,grandquista/rethinkdb,JackieXie168/rethinkdb,eliangidoni/rethinkdb,JackieXie168/rethinkdb,jmptrader/rethinkdb,bpradipt/rethinkdb,niieani/rethinkdb,mbroadst/rethinkdb,grandquista/rethinkdb,robertjpayne/rethinkdb,jmptrader/rethinkdb,grandquista/rethinkdb,eliangidoni/rethinkdb,bpradipt/rethinkdb,JackieXie168/rethinkdb,Qinusty/rethinkdb,niieani/rethinkdb,dparnell/rethinkdb