psql: Improve error display for psql -f -

Running "psql -f -" used to print

psql:<stdin>:1: ERROR:  blah

but that got broken between 8.4 and 9.0 (commit
b291c0fb), and now it printed

psql:-:1: ERROR:  blah

This reverts to the old behavior and cleans up some code that was left
dead or useless by the mentioned commit.

src/bin/psql/command.c

@@ -2062,15 +2062,18 @@ process_file(char *filename, bool single_txn, bool use_relative_path)
 		}
 
 		fd = fopen(filename, PG_BINARY_R);
-	}
-	else
-		fd = stdin;
 
 		if (!fd)
 		{
 			psql_error("%s: %s\n", filename, strerror(errno));
 			return EXIT_FAILURE;
 		}
+	}
+	else
+	{
+		fd = stdin;
+		filename = "<stdin>";	/* for future error messages */
+	}
 
 	oldfilename = pset.inputfile;
 	pset.inputfile = filename;

src/bin/psql/startup.c

@@ -313,8 +313,6 @@ main(int argc, char *argv[])
 			printf(_("Type \"help\" for help.\n\n"));
 		if (!pset.notty)
 			initializeInput(options.no_readline ? 0 : 1);
-		if (options.action_string)		/* -f - was used */
-			pset.inputfile = "<stdin>";
 
 		successResult = MainLoop(stdin);
 	}