New version of ScreenDemo.m and Screen.dll

I have attached to this message a new version of the ScreenDemo.m and
another release of SCREEN. ScreenDemo now steps through with key
presses instead of mouse clicks. This change was made because of the
GetClicks bug, where GetClicks does not detect mouse clicks after the
pixel size has been changed using the pixelSize argument to SCREEN
'OpenWindow'.

The accompanying version of SCREEN fixes these bugs:

-If a one-element matrix was passed as a color argument to SCREEN
along with a pointer to window with 32-bit pixels, SCREEN mishandled
the color value. The problem has been fixed.

-SCREEN 'PutImage' did not work correctly with 32 bit pixels. The
problem has been fixed.

-SCREEN 'GetImage' for 32-bit pixels has been implemented.

-SCREEN 'TextSize' returned values with inverted sign. The values are
now positive.


-- Allen