pgsql: Fix filtered_base_yylex() to save and restore base_yylval and

Log Message:
-----------
Fix filtered_base_yylex() to save and restore base_yylval and base_yylloc
properly when doing a lookahead.  The lack of this was causing various
interesting misbehaviors when one tries to use "with" as a plain identifier.

Modified Files:
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    pgsql/src/backend/parser:
        parser.c (r1.69 -> r1.70)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parser.c.diff?r1=1.69&r2=1.70)