pgsql: More incremental refactoring in plpgsql: get rid of gram.y

Log Message:
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More incremental refactoring in plpgsql: get rid of gram.y dependencies on
yytext. This is a necessary change if we're going to have a lexer interface
layer that does lookahead, since yytext won't necessarily be in step with
what the grammar thinks is the current token. yylval and yylloc should
be the only side-variables that we need to manage when doing lookahead.

Modified Files:
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pgsql/src/pl/plpgsql/src:
gram.y (r1.133 -> r1.134)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/gram.y?r1=1.133&r2=1.134)
pl_comp.c (r1.143 -> r1.144)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/pl_comp.c?r1=1.143&r2=1.144)
plpgsql.h (r1.122 -> r1.123)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/plpgsql.h?r1=1.122&r2=1.123)
scan.l (r1.75 -> r1.76)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/scan.l?r1=1.75&r2=1.76)