Improvement of background image bg.png

I have improved the sharp pixels of the background image.


Here is a comparison of the old background image and my improved version:

![background-comparison](https://f.cloud.github.com/assets/4200435/1698244/345b371e-5f3b-11e3-8767-dd88eeb418e9.png)


Note the sharpness of icons and text in the new background. The old sharp pixels of the background texture were interfering with text a bit, so I changed this for you and kept the same color.


The improved background image is here:

![bg](https://f.cloud.github.com/assets/4200435/1698246/59341c36-5f3b-11e3-8301-f071bb5759bb.png)


ImGur hosted file here:

http://i.imgur.com/CUWR3O0.png


My version is still the same 75px X 75px as the old one, but much slimmer with 1.702 bytes.


There seems to be no way to replace image files in pull requests, or the developers of Github made is super difficult to make image file replacements. So this pull request just erases the image. Take the new image and replace it manually, if you have privileges for that.