* Fail if mkbootimg/uboot-tools are not installed, but creating a
boot.img file / u-boot legacy image was requested via deviceinfo
(fixes#312)
* Fail if /boot/dt.img is missing, but we have a qcdt device
* Fail if the dtb file specified in deviceinfo does not exist
* Fail if mkbootimg etc. exit with error code
* Don't try to add the ext4 module into the initramfs. We always
compile it into the kernel. Instead, kconfig_check makes sure it
is enabled now. (fixes#1037)
* Add a note that modprobe warnings can be ignored mostly
