pgsql: parse_ident_usermap() shuold use ereport(LOG) and not ERROR, and

Log Message:
-----------
parse_ident_usermap() shuold use ereport(LOG) and not ERROR, and put the
return value in the *error_p variable.

Noted by Tom.

Modified Files:
--------------
pgsql/src/backend/libpq:
hba.c (r1.187 -> r1.188)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/hba.c?r1=1.187&r2=1.188)