Fixes to uninteded RGB<->BGR colorspace inversions during ndarray conversions

The expression ```np.array(self.getMatrix())``` where ```self``` is of type ```Image``` is a bug that causes an unintended colorspace inversion BGR->RGB (but the colorspace is invariant for RGB images).

Here is some code that exposes the bug, where ```img0``` should be equivalent to the ```img1``` but is not, violating the following identity transformations:
```python
from SimpleCV import *
img0 = Image("lenna").toBGR()
img1 = Image(img0.getNumpyCv2().swapaxes(0,1))
img1.save("blue_lenna.png")
```
and this *opposite* RGB->BGR inversion bug, likely caused by a short-sighted attempt to fix the previous bug:
```python
from SimpleCV import *
img0 = Image("lenna").toRGB()
img1 = Image(img0.getNumpy())
img1.save("blue_lenna.png")
```
I recommend a series of such "invariant" transformation tests as part of a unit testing framework.

These patches make the following changes:
- Fixes BGR->RGB inversion in the ```Image.getNumpyCv2``` by forcing conversion to RGB Image before conversion to a numpy array. 
 
- Fixes the *opposite* RGB->BGR inversion in the implementation of ```Image.getNumpy```, it has been changed by removing backwards slicing of the 3rd dimension and forcing the preliminary RGB conversion.

- All instances of the aforementioned problematic expression in the file ```ImageClass.py``` have been replaced by calls to these amended methods.

![blue_lenna](https://f.cloud.github.com/assets/1470227/307128/979123a0-96b1-11e2-90b4-c62135fed1ee.png)