#83 win32-gui-demos.pl does not run demos on Cygwin

[Yaakov Selkowitz]

win32-gui-demos.pl from Win32::GUI 1.12, built with Cygwin perl 5.22.1-1, starts and displays the demos' code as expected, but "Run demo" or double-clicking on the demo name does nothing. The issue is that a POSIX path is passed to ShellExecute, which only knows of Win32 paths.

I'm not sure, based on the typical use of Win32::GUI, if the proper solution is to use cygwin_conv_path in the ShellExecute wrapper (as found elsewhere in GUI.xs) or if win32-gui-demos.pl needs to call 'cygpath -w' on cygwin.