PHP 4.3 support and other improvements, see details

* Support for PHP 4.3
* Replace isset `isset($vector['var']{0})` by `isset($vector['var']) && strlen($vector['var'])>0` to prevent the error `Uninitialized string offset: 0`
* `MAX_EXEC` may not be less than 15 seconds
* Add support to bitmap files
* If the parameter "callback" has invalid characters then sets the variable `$param_callback` with `JSLOG`;
* Detects if the "host:" header was set by the client
* Remove port from `$_SERVER['HTTP_HOST']` to prevent problem in the formatting of the address
* Add function for remove old files