Made securityError more descriptive for OS X
Made securityError more descriptive for OS X

Modified securityError to use SecCopyErrorMessageString on OS X for a more descriptive error message.

Ninikitos/UICKeyChainStore,HSFGitHub/UICKeyChainStore,gauravds/UICKeyChainStore,hanhailong/UICKeyChainStore,bigrpg/UICKeyChainStore,TomoakiNagahara/UICKeyChainStore,hulu001/UICKeyChainStore,dleehr/UICKeyChainStore,dezinezync/UICKeyChainStore,kishikawakatsumi/UICKeyChainStore,imjerrybao/UICKeyChainStore,royalwang/UICKeyChainStore,Kingside/UICKeyChainStore,v2dev/UICKeyChainStore,kishikawakatsumi/UICKeyChainStore