pgsql: Fix pg_wchar_table's maxmblen field of EUC_CN, EUC_TW,

Log Message:
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Fix pg_wchar_table's maxmblen field of EUC_CN, EUC_TW, MULE_INTERNAL
and GB18030. patches from ITAGAKI Takahiro.

Modified Files:
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pgsql/src/backend/utils/mb:
wchar.c (r1.60 -> r1.61)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/mb/wchar.c.diff?r1=1.60&r2=1.61)