Check return code of uloop_run() and pass the signal number up when the
loop was interrupted. After cleanup, uninstall uloop's signal handlers
and re-raise the signal to terminate the process.
This allows interrupting the autoupdater using Ctrl-C during downloads,
instead of having it continue with the next mirror (if multple are
configured). As uloop's signal handlers only set a flag to interrupt
uloop_run() and have otherwise no effect, the autoupdater can still only
be interrupted during HTTP requests, ensuring we can't leave the system
in an inconsistent state.
X-FIRMWARE-VERSION gets set to the content of the file referenced by UCI setting "autoupdater.settings.version_file"
If "autoupdater.settings.version_file" is unset X-FIRMWARE-VERSION is
omitted
This new version of the autoupdater is implemented in C instead of Lua,
allowing us to interface with libuclient (HTTP downloads) and libecdsautil
(signature checks) directly instead of spawning external processes,
saving RAM and making error handling more robust.
[Matthias Schiffer: add commit message]
Matthias Schiffer