ftp/display: add function to move cursor vertically

When draw at the end of the window, we need to scroll up the window.

This patch add a function to scroll up the window when it is at the last two
line.

Also this fix a bug during getting the command line.
ftp/display: scroll the window in print_message

This patch fix a bug in print message functions. During print, it will scroll
up the window when the cursor is at the last 2 line.
ftp/display: make print_(v)message '\n' aware

Previously, print_(v)message will try to ignore the '\n' in the message.

This patch will update the cursor according to the message format.