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?

PBGitRepository.h

@@ -13,9 +13,13 @@
 	NSArray* commits;
 }
 
-+ (PBGitRepository*) repositoryWithPath:(NSString*) path;
 + (void) setGitPath;
+
++ (PBGitRepository*) repositoryWithPath:(NSString*) path;
+- (PBGitRepository*) initWithPath:(NSString*) path;
+
 - (NSFileHandle*) handleForCommand:(NSString*) cmd;
+- (void) initializeCommits;
 - (void) addCommit: (id)obj;
 
 @property (copy) NSString* path;