Merge branch 'jn/gc-auto'

"gc --auto" ended up calling exit(-1) upon error, which has been corrected to use exit(1). Also the error reporting behaviour when daemonized has been updated to exit with zero status when stopping due to a previously discovered error (which implies there is no point running gc to improve the situation); we used to exit with failure in such a case. * jn/gc-auto: gc: do not return error for prior errors in daemonized mode