apache_get_version() - depends on settings in httpd.conf ServerTokens
Examples:
ServerTokens Full - Apache/2.0.55 (Win32) DAV/2
ServerTokens OS - Apache/2.0.55 (Win32)
ServerTokens Minor - Apache/2.0
ServerTokens Minimal - Apache/2.0.55
ServerTokens Major - Apache/2
ServerTokens Prod - Apache