Let this commit serve as a warning about the perils of duck typing.
Word documents (docx,odt,etc) were being uncompressed when they were
attached to emails. The email importer now checks a list of well known
extensions and will not attempt to unzip them.
It is stuck using a list of extensions instead of using file magic because
many of these formats produce an application/zip mimetype when scanned.
seamus tuohy