Use GetMessagePos, not GetCursorPos to make sure we get the right mouse position...

Use GetMessagePos, not GetCursorPos to make sure we get the right mouse position. Also, no need to get mouse position at time of keypress, every mouse movement before the keypress is processed in an earlier WM_MOUSE message already, so mouse position in the window state is all we need.

git-svn-id: svn+ssh://svn.code.sf.net/p/freeglut/code/trunk/freeglut/freeglut@1515 7f0cb862-5218-0410-a997-914c9d46530a