added check that xcode-path return existing directory, to check xcode 4.3 command line tools install issue
added check that xcode-path return existing directory, to check xcode 4.3 command line tools install issue

x2on/OpenSSL-for-iPhone,oneton/OpenSSL-for-iPhone,x2on/OpenSSL-for-iPhone,ccwangzh/OpenSSL,ccwangzh/OpenSSL,oneton/OpenSSL-for-iPhone,oneton/OpenSSL-for-iPhone,x2on/OpenSSL-for-iPhone,x2on/OpenSSL-for-iPhone,ccwangzh/OpenSSL,ccwangzh/OpenSSL,ccwangzh/OpenSSL,ccwangzh/OpenSSL