[imp] Posible fix solution when attach files from Gollem

[Sebastián Calero]

If I attach a file from Gollem to a IMP message the MIME part is always 'application/octet-stream'. To determine the correct MIME type I change the 'addMIMEPartAttachment()' function in imp/lib/Compose.php like this:
<                     $type = MIME_Magic::filenameToMIME($attachment, false);
---
>                     $type = MIME_Magic::filenameToMIME($part->getName(), false);

Greetings...

Sebastian Calero.