support "with Vips.Image" in Python

though it doesn't actually do anything, it looks nice

ChangeLog

@@ -7,6 +7,7 @@
 - added bandand() bandor() bandeor() convenience funcs to Python
 - oops, base64 encode could pad by up to two zero bytes
 - added VipsRefString as a thing that gi bindings can unpack
+- support "with Vips.Image as ...:" in Python
 
 7/5/15 started 8.0.3
 - dzsave and tif pyr write could fail for some image dimensions, thanks Jonas

python/Vips.py

@@ -588,6 +588,12 @@ class Image(Vips.Image):
 
     # we can use Vips.Image.write_to_memory() directly
 
+    # support with in the most trivial way
+    def __enter__(self):
+        return self
+    def __exit__(self, type, value, traceback):
+        pass
+
     # operator overloads
 
     def __getattr__(self, name):