arrows sometimes flipped

[Richard Todd]

All,

I noticed when a machine is connected to another machine,
such that the arrow should point -->--, it sometimes 
faces the wrong way.  It only happens when the line
is completely horizontal (dy == 0).  I found the bug, 
and here's a cleaned up version of the code in 
engine_view.c:
-----------------------------------------------------
if (dy == 0) theta = ((dx<=0)?0:PI);
else {
   theta = atan(((double)dx)/((double)dy));
   theta = (PI/2.0) - theta;    // we want the complementary angle
   if (sy < ky)
        theta += PI; 
}

if(theta)
   poly_rotate(poly, 3, theta);

// now we can draw....
---------------------------------------------------

It fixes the flipping problem, and also combines the two
potential calls to poly_rotate() into one.

Nice to see the project picking up steam!

Richard Todd