Remove outside-the-scanner references to "yyleng".

It seems the flex developers have decided to change yyleng from int to size_t.
This has already happened in the latest release of OS X, and will start
happening elsewhere once the next release of flex appears.  Rather than trying
to divine how it's declared in any particular build, let's just remove the one
existing not-very-necessary external usage.

Back-patch to all supported branches; not so much because users in the field
are likely to care about building old branches with cutting-edge flex, as
to keep OSX-based buildfarm members from having problems with old branches.

src/interfaces/ecpg/preproc/extern.h

-/* $PostgreSQL: pgsql/src/interfaces/ecpg/preproc/extern.h,v 1.70 2007/11/15 21:14:45 momjian Exp $ */
+/* $PostgreSQL: pgsql/src/interfaces/ecpg/preproc/extern.h,v 1.70.2.1 2009/09/08 04:25:25 tgl Exp $ */
 
 #ifndef _ECPG_PREPROC_EXTERN_H
 #define _ECPG_PREPROC_EXTERN_H
@@ -38,8 +38,7 @@ extern char *yytext,
 #ifdef YYDEBUG
 extern int	yydebug;
 #endif
-extern int	yylineno,
-			yyleng;
+extern int	yylineno;
 extern FILE *yyin,
 		   *yyout;
 extern char *output_filename;

src/interfaces/ecpg/preproc/preproc.y

-/* $PostgreSQL: pgsql/src/interfaces/ecpg/preproc/preproc.y,v 1.359.2.6 2008/10/10 12:20:06 meskes Exp $ */
+/* $PostgreSQL: pgsql/src/interfaces/ecpg/preproc/preproc.y,v 1.359.2.7 2009/09/08 04:25:25 tgl Exp $ */
 
 /* Copyright comment */
 %{
@@ -173,11 +173,7 @@ make3_str(char *str1, char *str2, char *str3)
 static char *
 make_name(void)
 {
-	char * name = (char *)mm_alloc(yyleng + 1);
-
-	strncpy(name, yytext, yyleng);
-	name[yyleng] = '\0';
-	return(name);
+	return mm_strdup(yytext);
 }
 
 static char *