pgsql: Print combining characters (those reported as having zero width

Log Message:
-----------
Print combining characters (those reported as having zero width by
PQdsplen()) normally, instead of replacing them by \uXXXX sequences.
Assume that they in fact occupy zero screen space for formatting purposes.
Per gripe from Michael Fuhr and ensuing discussion.

Modified Files:
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pgsql/src/bin/psql:
mbprint.c (r1.23 -> r1.24)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/mbprint.c.diff?r1=1.23&r2=1.24)