don't take the min size into account when setting the window size explicitly in wxGTK...

don't take the min size into account when setting the window size explicitly in wxGTK, just as wxMSW doesn't do it; mention this in the docs and added a unit test to enforce this

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@53741 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775