#264 Include option for single instance of Dev-C++

[jaegen]

I would like to be able to launch Dev-C++ from a
different IDE, and have it detect and restore a previous
instance of Dev, rather than launching a completely new
instance. Currently, if I double click on a properly
associated file in Windows Explorer (*.cpp etc.), it does
detect a previous instance, but if I launch it from an IDE
(passing file name argument on the command-line), it
launches a new instance each time.