Bug-fix: when exporting FTN netmail from SMB "mail" base, if the netmail

included an "old-style" (not MIME-encoded) file attachment (where the file path
is in the subject and the FILEATTACH aux-attribute flag is set), the
corresponding netmail attribute flag would not be set in the stored msg (*.msg)
file. Also simplified the create_netmail() function prototype/usage, removing
the "file_attached" argument (use the hdr.auxattr instead).