Make the window actually occupy the full screen in full-screen mode (without this...

Make the window actually occupy the full screen in full-screen mode (without this, other windows, such as the taskbar on Linux, will display in front of it.). Additional fixes for various full-screen mode issues (Setting FullScreen checkbox in options menu had no effect,  null pointer, etc.  When fullScreen and scaling options are changed simultaneously in the dialog, collapse the viewport changes into a single operation.  There is still a modality issue on OS-X that will be addressed in a later patch.

git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@4970 3789f03b-4d11-0410-bbf8-ca57d06f2519