GLVertexBuffer::addUniform unfinished GLMatrix support

[John]

I was writing a shader for a compiz plugin, and couldn't work out why my matrices uniforms were not working. A few hours later of test-apps and digging through the compiz source I found:

```
bool GLVertexBuffer::addUniform (const char *name, const GLMatrix &value)
{
    //#warning Add 'addUniform' support to GLMatrix type !
    return true;
}
```

I would expect this to: (a) fail loudly, perhaps printing a warning to the console or (b) actually work! :-)

Fixing it looks to be a simple case of making a new Uniform<double, 16> and copying the GLMatrix into it. Best guess is this would do the trick...

Line 250 vertexbuffer.cpp
```
void GLVertexBuffer::addUniform (const char *name, GLMatrix &value)
{
    // we're casting to double here to make our template va_arg happy
    Uniform<double, 16>* uniform = new Uniform<double, 16>(name,
        (double)value[0], (double)value[1], (double)value[2], (double)value[3],
        (double)value[4], (double)value[5], (double)value[6], (double)value[7],
        (double)value[8], (double)value[9], (double)value[10], (double)value[11],
        (double)value[12], (double)value[13], (double)value[14], (double)value[15]);
    priv->uniforms.push_back (uniform);
}
```

Line 85 privatevertexbuffer.h
```
case 16: {
    GLMatrix m;
    for (int i = 0; i < 16; ++i)
        m[0] = (float)a[0];
    prog->setUniform (n, m);
    break;
}
```