[CONFSERVER-18951] Fix mime type for attachment file uploads.

For certain file types the mime type is not not correct when uploading an attachment.
E.g. IE 6 uses "application/x-zip-compressed" for docx files.

The drag 'n drop upload has a similar problem.

is related to

CONFSERVER-17718 Downloading a .docx file in IE7/WinXP gives it a .zip extension (technically true but the average end-user wouldn't know that).

CONFSERVER-18580 MIME types issues with "drag and drop" method in Confluence 3.1

CONFSERVER-19045 Downloading an Excel Microsoft Office 2007 file in IE7/WinXP gives it a .zip extension.

CRUC-4489 Using Attachment option doesn't work with Chrome

CONFSERVER-10506 Guess MIME types for objects uploaded as application/octet-stream

relates to

CONFSERVER-18766 PDF attachments with uppercase extension have wrong content type in Firefox

CONFSERVER-21706 Add OpenOffice mime type for attachment file uploads.

(2 relates to)