run_command(): respect GIT_TRACE

When GIT_TRACE is set, the user is most likely wanting to see an external
command that is about to be executed.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

run-command.c

@@ -65,6 +65,8 @@ int start_command(struct child_process *cmd)
 		cmd->err = fderr[0];
 	}
 
+	trace_argv_printf(cmd->argv, "trace: run_command:");
+
 	cmd->pid = fork();
 	if (cmd->pid < 0) {
 		if (need_in)