Fixed child process signal behaviours. (#128)

* Restored signal handlers upon fork().
* Improved error handling of hpfs process kill scenario.
* Set pgid for forked processes for graceful sending of SIGINT.

src/comm/comm_server.cpp

@@ -295,7 +295,7 @@ namespace comm
         else if (pid == 0)
         {
             // Websocketd process.
-            util::unmask_signal();
+            util::fork_detach();
 
             // We are using websocketd forked repo: https://github.com/codetsunami/websocketd