post-build.sh: cleanup warning message on rm

It wasn't a problem, but was cluttering the output.
erlinit: bump to v0.3.0
new package: blstrobe

This utility communicates with BenQ monitors via the DDC bus to control
backlight flicker timing.
rpi_qt5: add config supporting qt5 and webkit

This also bumps the rootfs max size to 128 MB like specified in
fwtool.config in the comments.
Pull in latest buildroot, bump RPi kernel
Launch dtach for qt5 so that termin can be in gui
nerves.mk: alternative to sourcing nerves-env.sh

For Nerves configurations that pull in Nerves as a subdirectory to the
project, this file can be included in a Makefile to achieve similar
results as sourcing nerves-env.sh.