**/Makefile.kmk: Cosmetic changes.
HostServices/SharedClipboard/testcase: re-enable Windows
HostServices/SharedClipboard: setter for headless mode in service, ignored at present
HostServices/SharedClipboard/testcase: disable Windows for now
GuestHost/SharedClipboard: moved the RTEnvGet("DISPLAY") hack out into the host-specific code, missed files