Add changes to support Saskatoon Amiga Users Group BBS.

- Support LCF (Last Column Flag) mode per DEC STD-070
  (Despite years of protest that it's stupid)
- "Properly" support CSI 7 m and CSI 27 m
  Now, when in "Negative Image" mode, changes to the foreground
  change how the background is drawn and vice-versa.  Perviously
  this command just swapped the two values and called it good.