ui/curses: Support line graphics chars on -curses mode

This converts vga code to curses code in console_write_bh().

With this changes, we can see line graphics (for example, dialog uses)
correctly.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>