Revise checks for "filename" directive element in read_directive_file

Revise checks for "filename" directive element in read_directive_file

The revised code uses the "filename" directive element as a command to
install an uploaded file.  This change ensures that a legitimate loose
directive will be processed even if accompanied with a bogus file.

This is a definitive break from protocol version 1.0, which was disabled
in 2012 and recently removed.