#163 incorrect mime type on renamed .msi files

[Wes Risenmay]

Using the magic mime type identifier to evaluate the mime type of an msi .xls extension results in a mime type of "application/vnd.ms-office". The mime type should be "application/octet-stream".

Steps to reproduce:

1. Find a .msi file.
2. rename the extension to .xls
3. Use MagicMimeTypeIdentifier to identify the mime type
4. observe that the mime type is incorrect