protect from NPE
small cleanup
simplify ErlRuntime
rpcs fail faster now if backend is down (no timeout, just throw exception directly)
try to handle restart better
report backend down with dialog only for internal backends
make RuntimeInfo immutable and use builder to construct it
remove runtime.api plugin
move backend extension point to backend.api; now runtime plugin is completely independent of eclipse
reorganize backend.api classes
fix plugin manifests
cleanup code
simplify IBackendProvider