参看原帖：
http://stackoverflow.com/questions/6475727/why-does-static-nsstring-leak
报错信息：
objc[4501]: Object 0x6e17060 of class __NSCFString autoreleased with no pool in place - just leaking - break on objc_autoreleaseNoPool() to debug
objc[4501]: Object 0x6e12470 of class NSPathStore2 autoreleased with no pool in place - just leaking - break on objc_autoreleaseNoPool() to debug
objc[4501]: Object 0x6e12580 of class __NSCFData autoreleased with no pool in place - just leaking - break on objc_autoreleaseNoPool() to debug