Theme API break for button borders

[Eric Wasylishen]

Hi,
I made a small change to the theme API yesterday:

- (NSSize) buttonBorderForCell: (NSCell*)cell
                                  style: (int)style 
                                  state: (GSThemeControlState)state;

is changed to:

typedef struct GSThemeMargins
{
  CGFloat left;
  CGFloat right;
  CGFloat top;
  CGFloat bottom;
} GSThemeMargins;

- (GSThemeMargins) buttonMarginsForCell: (NSCell*)cell
                                  style: (int)style 
                                  state: (GSThemeControlState)state;

Now we can properly handle buttons where the content area's margins are 
different on all four sides.

I also made a slight adjustment to the metrics for the default NeXT-style 
button: instead of a 3pt border on all sides, it now has a 2 pt border on the 
top and left and 3pt on the right and bottom. This better matches how the 
button looks, and fixes the problem of scroller arrows looking off-center. 
Hopefully this doesn't cause too problems for anyone, but if it does, we can 
revert it.

Eric