Fix line-at-a-time mode printfile() operation with regards to attributes

maintained between lines, reported by Immortal@IDOMAIN:
Use P_SAVEATR to retain the new attributes after each call to putmsg() in
printfile() line-at-a-time mode. We are no setting the initial attribute to
LIGHTGRAY or restoring the original attribute at the end (like a call to
putmsg() withou the P_SAVEATR would) - so we may need to add that later
for line-at-a-time mode, as well.