Launching only one instance of SpeedCrunch

[AlexHalogen]

Each press on the calculator key on the keyboard or each double click on SpeedCrunch launches a new instance of SpeedCrunch(version 0.12). Can you add an option to let users decide whether to allow multiple instances? Operating system is windows 7 x64.

[Pol Welter]

Whatever way we go, people always request the other one.

See issues #556, #529, #363.

[Helder Correia]

I think we should go back to raising the existing instance and then adding a New Window menu command under Session.

[Michael Strelnikov]

It was much better with 0.11 - one instance only.

[Helder Correia]

Duplicate of #740.