added thread safety for prime number generation
added thread safety for prime number generation

anatoliyrazin/primesieve,ZahidDev/primesieve,kimwalisch/primesieve,anatoliyrazin/primesieve,tempbottle/primesieve,fredwang00/primesieve,fredwang00/primesieve,ZahidDev/primesieve,anatoliyrazin/primesieve,fredwang00/primesieve,ZahidDev/primesieve,tempbottle/primesieve,kimwalisch/primesieve,kimwalisch/primesieve,tempbottle/primesieve