This example demonstrates texture wrapping and clamping in the U and V
dimensions.  A quad is drawn, and texture coordinates may be selected -
one set of coordinates (the default) are in the unit square, and will not be
affected by the wrapping mode.  The other set of UVs are outside of the unit
square in both dimensions, and will exhibit different behavior, depending on
the wrapping mode.  The texture is chosen from a set of two, so that the
exact nature of wrapping and clamping may be explored

The key commands are:

h - switch horizontal texture wrapping (wrapping or clamping)
v - switch vertical texture wrapping (wrapping or clamping)
t - change texture image
c - change texture coordinates
