Add output flushing before fork()

This adds fflush(NULL) before fork() in start_command(), to keep
the generic interface safe.

A remaining use of fork() with no flushing is in a comment in
show_tree(). Rewrite that comment to use start_command().

Signed-off-by: Anders Melchiorsen <mail@cup.kalibalik.dk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-ls-tree.c

@@ -66,17 +66,16 @@ static int show_tree(const unsigned char *sha1, const char *base, int baselen,
 		/*
 		 * Maybe we want to have some recursive version here?
 		 *
-		 * Something like:
+		 * Something similar to this incomplete example:
 		 *
 		if (show_subprojects(base, baselen, pathname)) {
-			if (fork()) {
-				chdir(base);
-				exec ls-tree;
-			}
-			waitpid();
+			struct child_process ls_tree;
+
+			ls_tree.dir = base;
+			ls_tree.argv = ls-tree;
+			start_command(&ls_tree);
 		}
 		 *
-		 * ..or similar..
 		 */
 		type = commit_type;
 	} else if (S_ISDIR(mode)) {

run-command.c

@@ -68,6 +68,7 @@ int start_command(struct child_process *cmd)
 	trace_argv_printf(cmd->argv, "trace: run_command:");
 
 #ifndef __MINGW32__
+	fflush(NULL);
 	cmd->pid = fork();
 	if (!cmd->pid) {
 		if (cmd->no_stdin)