[Kst] [Bug 121108] Kst assertion failure when line or arrow moved outside of window

[Barth Netterfield]

George's patch works, with the following caveat:
	-Drag the end point out of the left side of the window and release.
	 The Y value of the end point is where you released it, but the X value is at 
the edge of the window.  So: the angle of the line changes.  Better behavior 
is to set X to the edge of the window, and to interpolate Y so the angle 
stays the same.

AFAIKT, this is what Andrew's patch did, but I haven't tried it due to white 
space mangling.

George, can you split out your "viewline object doesn't track moves 
 properly" patch so we can put that in.