Fix to resize correctly when source image.Bounds().Min is not (0,0)

Resizing an image with `image.Bounds().Min` not being (0,0) caused undesired effects.
This small change will add Min.Y as offset when calling filter.Interpolate()

The second round of resize has the xoffset, yoffset set to 0, 0 because it is them operating on the tempImg that has `tempImg.Bounds().Min` being (0,0).

The bug was noticed when doing a `resize.Resize()` after using `rgbaimage.SubImage()`

**Before fix:**
![539e66d6726fbf1a18000001](https://cloud.githubusercontent.com/assets/1511218/3283148/1bf29836-f50c-11e3-8e2b-3677b333cbf0.jpg)

**After fix:** (with a slightly different SubImage Rectangle, but you get the point)
![539e68d4726fbf192c000001](https://cloud.githubusercontent.com/assets/1511218/3283151/359d4cea-f50c-11e3-8c4a-58f9fc8792c6.jpg)