Bug fixes and enhancements

- Fixed calling PHP function with NULL parameter
- Fixed IdenticalOperator not working with LONG check
- Fixed DeclareStatement issuing a warning when declaring a variable
without default value
- Fixed scanner not tokenizing _COOKIE
- Added function calls with up to 8 parameters
- Checks that kernel is at the last version and update if necessary
- Optimize compilation by checking what needs to be compiled
- Refactored Commands into a command interface
- Added command clean