Improve names for cons25 sequences.

In a recent commit, I forgot to expand an X to an abbreviation of "BORDER".
Fix this and some nearby bad names.

The descriptions were copied from comments in scterm-sc.c, but some
of these are bad. The border [color] was inconsistently described as
a property of the "display", but I had changed this to "adapter" to
match the descriptions for other color settings. All colors supported
by the cons25 sequences are actually properties of the current vty and
that should not be described. But the other colors are defaults.
Change "adapter" to "default" for them and remove "adapter" for the
border. Reduce the verbosity of the abbreviation from AD to D.