vim: Prevent `set background=dark` from being reset

The call to `<SID>X("Normal", s:foreground, s:background, "")` resets
the background option and since VIm fails to detect the dark background
it gets set to `light`.

Moving the `set background=dark` call at the end fixes it.
Merge pull request #200 from em-/vim

vim: Prevent `set background=dark` from being reset
first commit
fixed typos
Merge pull request #201 from idleberg/master

Added missing themes
Add Tomorrow Night Eighties for Xcode 4
Merge pull request #202 from joemasilotti/master

Add Tomorrow Night Eighties for Xcode 4
Add GitGutter icon coloring
Update README with fork details

+Add fork and modification description and screenshot