Streamline terminal character write and ACS table construction routines.
Don't use ACS characters when it's not necessary (the external charset
already contains the required characters); this helps with
$_external_charset="cp437" on xterm -k8 -font vga (Putty makes no difference).
Only use ACS characters that are specified by the relevant terminfo entry.


git-svn-id: https://dosemu.svn.sourceforge.net/svnroot/dosemu/trunk@1573 7758b857-130e-0410-ab9c-d8735a528d18