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] )| 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. |
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