- Cleaned up default .mk files.

 - Removed erroneously checked-in "drilbo-test" binary from repository.

 - Added inline image test.
 - Implemented "setup_callback" and "wait_for_callback" functions,
   allowing the test main to re-use the code.
 - Adapted "display_zimage_on_X11" function to new parent window parameter,
   using own XTerminal window id if present for the inline test.

 - Implemented "parent_window" parameter in "display_zimage_on_X11"
   function, allowing parent window to be specified.
 - Implemnted centering of image in non-root parent window.

 - Altered "display_zimage_on_X11" function to include "parent_window"
   parameter which allows specifciation of the parent window to be used.

 - Added test images using binary import.