git-gui: Remove unnecessary space between columns in blame viewer
On Mac OS X the OS has "features" that like to draw thick black borders around the text field that has focus. This is nice if you want to know where your text is going and are blind as a bat, but it isn't the best thing to have in a table that is being faked through the abuse of Tk text widgets.
By setting our takefocus, highlightthickness and padx/y we can get rid of this border and get our text widgets packed right next to each other, with no padding between them. This makes the blame background color smoothly run across the entire line of commit data, line number and file content.
Signed-off-by: Shawn O. Pearce <email@example.com>