perl, python, ruby: Fix comments on call to close method.

Make the comments consistent.

Also make the Perl example call $g->close explicitly so it is
consistent with the other examples.

python/examples/create_disk.py

@@ -51,4 +51,7 @@ g.mkdir ("/foo")
 # the disk image.
 g.upload ("/etc/resolv.conf", "/foo/resolv.conf")
 
+# Note also that handles are automatically closed if they are
+# reaped by reference counting.  You only need to call close
+# if you want to close the handle right away.
 g.close ()