Make a grain boundary by rotating the current crystal in two different 
orientations and put the two copies of the crystal together.  Can be
used to create certain types of grain boundaries.  Not a general utility.

Usage: <tt>input = [ <i>gb_type sx0 sy0 p q shift_x shift_y shift_z</i> ] makegrainboundary </tt>

<p>
<tt><i>gb_type</i></tt> has to be non-zero.  The two crystals are rotated from the
parent crystal around the z-axis by angle &alpha; and -&alpha;, respectively, 
where arctan(&alpha;) = <tt><i>p</i></tt>/<tt><i>q</i></tt>.  <tt><i>sx0, sy0</i></tt>
specify the center of the rotation.  The plane sx = <tt><i>sx0</i></tt> is also
the boundary between the two crystals.  So the grain boundary thus created is
a pure tilt boundary.

<p>
WARNING: the values of <tt><i>shift_x, shift_y, shift_z</i></tt> are currently ignored?

<p>
For details, ask Hark Lee.
