Load commit list in a separate thread

This makes the initial startup much faster. Commits get loaded in a separate
thread, and are displayed every 1000 commits.

There is a bug in here that makes fails a click while it is loading the commit
list. Not sure how to fix this, perhaps send the arrayController?

PBWebGitController.h

@@ -8,15 +8,17 @@
 
 #import <Cocoa/Cocoa.h>
 #import "GitTest_AppDelegate.h"
+#import "PBGitCommit.h"
 #import <WebKit/WebKit.h>
 
 @interface PBWebGitController : NSObject {
 	IBOutlet GitTest_AppDelegate* controller;
 	IBOutlet WebView* view;
 	IBOutlet NSArrayController* commitsController;
+	NSString* currentSha;
 	NSString* diff;
 }
 
-- (void) changeContentTo: (id) content;
+- (void) changeContentTo: (PBGitCommit *) content;
 @property (readonly) NSString* diff;
 @end