* the MouseIsVisible global variable from the go32v2 mouse unit moved to the
  implementation part. Reasons for making it private:
  1) its value is inaccurate when the mouse cursor is drawn by the int 33h mouse
     driver (which is the case e.g. in the standard 80x25 and 80x50 vga text
     modes, so quite a common case) and there's no way to make it accurate
     (there's no function to read the mouse driver's internal 'hide counter')
  2) code using this variable to hide the cursor temporarily before updating the
     screen directly should instead always call HideMouse before updating and
     ShowMouse after updating, thus relying on the mouse driver's hide count to
     restore the mouse cursor to its original state
  3) this variable is go32v2 specific and looks like it was meant only for
     internal use anyway. It was only used by the go32v2 video unit when
     updating the screen, but that was changed due to 2)

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@29066 3ad0048d-3df7-0310-abae-a5850022a9f2