Catch wallet file related exceptions in Qt wizard.

lib/util.py

@@ -84,6 +84,12 @@ class TimeoutException(Exception):
         return self.message
 
 
+class WalletFileException(Exception): pass
+
+
+class BitcoinException(Exception): pass
+
+
 # Throw this exception to unwind the stack like when an error occurs.
 # However unlike other exceptions the user won't be informed.
 class UserCancelled(Exception):