Following up on a forums post, make sure that if AllowFilter is used on
SFTP uploads, that the allowed file can be created AND written to.  The latter
part was failing because of the format of WRITE requests, and assumptions
made by the AllowFilter-checking code.
Merge pull request #70 from proftpd/sftp-allowfilter-redux

Following up on a forums post, make sure that if AllowFilter is used on