pgsql: Avoid passing signed chars to <ctype.h> functions ...

Log Message:
-----------
Avoid passing signed chars to <ctype.h> functions ... same old
portability mistake as always. Per buildfarm member pika.

Modified Files:
--------------
pgsql/src/bin/psql:
command.c (r1.228 -> r1.229)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/command.c?r1=1.228&amp;r2=1.229)