runtime error running test\main.nim:   compile with -d:nimOldCaseObjects
on win10
Nim Compiler Version 1.4.2 [Windows: amd64]
```
...\nimx\test\main.nim(68, 26): RUNNING sendMouseDownEvent(mainWindow, newPoint(50, 60))
...\nimx\test\main.nim(69, 24): RUNNING sendMouseUpEvent(mainWindow, newPoint(50, 60))
...\nimx\test\main.nim(92) main
...\.nimble\pkgs\nimx-0.1\nimx\private\windows\sdl_window.nim(555) runUntilQuit
...\.nimble\pkgs\nimx-0.1\nimx\private\windows\sdl_window.nim(505) nextEvent
...\.nimble\pkgs\nimx-0.1\nimx\private\windows\sdl_window.nim(433) handleEvent
...\.nimble\pkgs\nimx-0.1\nimx\image.nim(469) loadComplete
...\.nimble\pkgs\nimx-0.1\nimx\assets\asset_cache.nim(9) :anonymous
...\.nimble\pkgs\variant-0.2.9\variant.nim(194) newVariant
...\nim\lib\system\assign.nim(292) FieldDiscriminantCheck
...\nim\lib\system\fatal.nim(49) sysFatal
Error: unhandled exception: assignment to discriminant changes object branch; compile with -d:nimOldCaseObjects for a transition period [FieldDefect]
Error: execution of an external program failed: '...\nimx\test\main.exe '
```
(Note:  I have replaced the actual directories with  ...\ )

Compiling with `-d:nimOldCaseObjects`  fixes the problem so that the tests run, but I don't know if there are further flow-on effects.  There are some event/clicking issues on my system, but that might be related to #264 
