php_version  常量 显示出当前php版本  同 phpversion（）函数功能相同
phpinfo()函数 可以带个int类型的参数
以下来源php手册： 
bool phpinfo ( [int what] )
name (constant) value description
info_general 1 the configuration line, php.ini location, build date, web server, system and more.
info_credits 2 php credits. see also phpcredits().
info_configuration 4 current local and master values for php directives. see also ini_get().
info_modules 8 loaded modules and their respective settings. see also get_loaded_extensions().
info_environment 16 environment variable information that's also available in $_env.
info_variables 32 shows all predefined variables from egpcs (environment, get, post, cookie, server).
info_license 64 php license information. see also the license faq.
info_all -1 shows all of the above. this is the default value.