pgsql: Write to the Windows eventlog in UTF16, converting the message

Log Message:
-----------
Write to the Windows eventlog in UTF16, converting the message encoding
as necessary.

Itagaki Takahiro with some changes from me

Modified Files:
--------------
pgsql/src/backend/utils/error:
elog.c (r1.217 -> r1.218)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/error/elog.c?r1=1.217&r2=1.218)
pgsql/src/backend/utils/mb:
encnames.c (r1.39 -> r1.40)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/mb/encnames.c?r1=1.39&r2=1.40)
mbutils.c (r1.89 -> r1.90)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/mb/mbutils.c?r1=1.89&r2=1.90)
pgsql/src/include/mb:
pg_wchar.h (r1.91 -> r1.92)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/mb/pg_wchar.h?r1=1.91&r2=1.92)