IPC-server hardening and update

- add IMPLEMENT_RANDOMIZE_STACK for ipcThread()
- log / print boost interprocess exceptions
- use MAX_URI_LENGTH in guiconstants.h (also used in qrcodedialog.cpp)
- remove unneeded includes and ipcShutdown() from qtipcserver.cpp
- fix a small mem-leak by deleting mq before re-using it
- make ipcThread() and ipcThread2() static functions
- add some more comments

src/qt/guiconstants.h

@@ -4,10 +4,10 @@
 /* Milliseconds between model updates */
 static const int MODEL_UPDATE_DELAY = 500;
 
-/* Maximum  passphrase length */
+/* AskPassphraseDialog -- Maximum passphrase length */
 static const int MAX_PASSPHRASE_SIZE = 1024;
 
-/* Size of icons in status bar */
+/* BitcoinGUI -- Size of icons in status bar */
 static const int STATUSBAR_ICONSIZE = 16;
 
 /* Invalid field background style */