core: print line for include_file errors

- easier to localize the error, reported by Raul Alexis Betancor Santana

cfg.lex

@@ -1249,7 +1249,10 @@ SUBST       subst
 <INCLF>[ \t]*      /* eat the whitespace */
 <INCLF>[^ \t\n]+   { /* get the include file name */
 				if(sr_push_yy_state(yytext)<0)
+				{
+					LOG(L_CRIT, "error at %s line %d\n", (finame)?finame:"cfg", line);
 					exit(-1);
+				}
 				BEGIN(INITIAL);
 }