pgsql: In new "invalid byte sequence" error hint, call it "error", not

Log Message:
-----------
In new "invalid byte sequence" error hint, call it "error", not
"failure".

Modified Files:
--------------
pgsql/src/backend/utils/mb:
wchar.c (r1.56 -> r1.57)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/mb/wchar.c.diff?r1=1.56&r2=1.57)