Added Image.GetCurrent()

Previously the only way to get the current image was flaky and relyd on the image being assigned to a mesh.

try:
  me = Scene.GetCurrent().getAttiveObject().getData(mesh=1)
  image = me.faces[me.activeFace].image
except:
  image = None

...Can new be replaced by the following, and works even when there is no mesh.
image = Image.GetCurrent()

epydocs:
  Get the currently displayed Image from Blenders UV/Image window.
  When multiple images are displayed, the last active UV/Image windows image is used.

source/blender/python/api2_2x/doc/Image.py

@@ -52,6 +52,13 @@ def Get (name = None):
       - (): A list with all Image objects in the current scene.
   """
 
+def GetCurrent ():
+  """
+  Get the currently displayed Image from Blenders UV/Image window.
+  When multiple images are displayed, the last active UV/Image windows image is used.
+  @rtype: Blender Image
+  @return: The Current Blender Image, If there is no current image it returns None.
+  """
 
 class Image:
   """