flashcast: add eureka_images directory support
flashcast: fix outdated comment
flashcast: don't require imager.sh to be executable
flashcast: use "set -e" when appropriate in stock mods
flashcast: remove shebang lines from stock mods
basic: add gz and xz support to tar
flashcast: add missing underscore prefix to IMAGE_PATH in flash-image
flashcast: clean up mods after flashing to reduce memory usage