When register more than two interfaces only first two works

Put this into bootstrap and anly Uploadify and HTML4 upload will work.

``` php
MultipleFileUpload\MultipleFileUpload::getUIRegistrator()
    ->clear()
    ->register('MultipleFileUpload\UI\HTML4SingleUpload')
    ->register('MultipleFileUpload\UI\Uploadify')
    ->register('MultipleFileUpload\UI\SwfUpload')
    ->register('MultipleFileUpload\UI\Plupload');
```
