Bitcoin-Qt: give testnet a unique IPC message queue name

- this prevents an interference with the IPC message queue (which is used
  for URI processing) when running a testnet and mainnet instance in
  parallel
- to check for testnet, I had to raise the ParseParameters() call in
  main() to the topmost position
Merge pull request #2147 from Diapolo/mq_name_testnet

Bitcoin-Qt: give testnet a unique IPC message queue name