Added async submodule, formerly required by gitdb (which is still a valid submodule just yet)

Author: Byron

.gitmodules

@@ -2,3 +2,6 @@
 	path = git/ext/gitdb
 	url = git://github.com/gitpython-developers/gitdb.git
 	branch = master
+[submodule "git/ext/async"]
+	path = git/ext/async
+	url = git://github.com/gitpython-developers/async.git

git/__init__.py

@@ -14,12 +14,12 @@
 #{ Initialization
 def _init_externals():
 	"""Initialize external projects by putting them into the path"""
-	sys.path.append(os.path.join(os.path.dirname(__file__), 'ext', 'gitdb'))
+	sys.path.append(os.path.join(os.path.dirname(__file__), 'ext', 'async'))
 
 	try:
-		import gitdb
+		import async
 	except ImportError:
-		raise ImportError("'gitdb' could not be found in your PYTHONPATH")
+		raise ImportError("'async' could not be found in your PYTHONPATH")
 	#END verify import
 
 #} END initialization