[syslinux] Confusing error message when pointing the linux installer at a missing directory.

[Jack Kelly]

Last night, I was trying to install syslinux (5.01) to a SD card of
mine, writing to a subdirectory to keep the layout neat:

syslinux-5.01/linux# ./syslinux -i -d /boot /dev/mmcblk0p1
/dev/mmcblk0p1: No such file or directory

The message is coming from do_open_file() in syslinux.c: the call to
open() fails because the containing directory isn't present, and then it
calls perror(opt.device).

If the directory is present, syslinux installs and will boot. It's just
a matter of either improving the error message or trying to make the
directory before populating it.

-- Jack