chasquid: Check result of initial os.Chdir

The daemon attempts to change to the config directory on startup, for
security and convenience.

We currently don't check if this works, which is not a big deal since it
will just fail later on when it can't find the files. However, it makes
things more awkward to debug, so this patch adds an explicit check.

chasquid.go

@@ -81,7 +81,10 @@ func main() {
 	// It also can be useful in unusual environments and for testing purposes,
 	// where paths inside the configuration itself could be relative, and this
 	// fixes the point of reference.
-	os.Chdir(*configDir)
+	err = os.Chdir(*configDir)
+	if err != nil {
+		log.Fatalf("Error changing to config dir %q: %v", *configDir, err)
+	}
 
 	initMailLog(conf.MailLogPath)