4.4BSD snapshot (revision 8.1); add 1993 to copyright

src not being incremented, and string not null-terminated
from Chris Demetriou

don't check isascii(), check against UCHAR_MAX (see ANSI C, 4.3)
don't pass chars to library functions

strvis couldn't handle empty strings; from Christos for csh(1)

Add include files to get prototype declarations, and fix bugs found.

new implementation -- vis replaces cencode

(first half of) new version. name changes to vis() and unvis()

date and time created 89/10/13 16:00:08 by marc