Detect attachments with Content-Type: ...; name=

[RFC2045](http://www.ietf.org/rfc/rfc2045.txt), section 5.1 seems to indicate that arbitrary parameters can be appended to a Content-Type header specification. Some email clients seem to use the Content-Type header to specify an attachment without giving a separate Content-Disposition header normally used to signify attachments.

This patch corrects attachment detection for piped emails to detect such attachments. The patch also correctly decodes filenames specified either in the Content-Disposition or Content-Type headers using [RFC5987](http://tools.ietf.org/html/rfc5987), where the filename can be encoded using an arbitrary character set (ie, not us-ascii).