[dev] [dvtm] ESC sequences in madtty.c

 Hi,

I'm no terminal expert, and I'm reluctant to add more code to the
madtty.c source, but I hope these changes will be considered. They
certainly work for me!

The existing ESC ] s (CUPSV) and ESC ] u (CUPRS) are for save/restore
cursor position. I use at least one program that uses ESC 7 (DECSC) and
ESC 8 (DECRC) to save/restore state, both cursor position and character
attributes, so I've implemented them. To do this, I created reusable
functions for save_curs(), restore_curs(), save_attrs(), and
restore_attrs() because they are used more than once now.

I also have some programs that were displaying weird reverse video
backgrounds, only in dvtm. To fix this I added code at the beginning and
end of the interpret_csi_ED() 'erase display' function so that the
display is always erased with A_NORMAL character attributes.

Thanks! --Ross