[glibmm] Gio::PollableInput/OutputStream: Comments about base classes.

[Murray Cumming <murrayc src gnome org>]

commit 61c781204d1080bad1679e1db4f40b986157c079
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Dec 2 12:13:06 2016 +0100

    Gio::PollableInput/OutputStream: Comments about base classes.

 gio/src/pollableinputstream.hg  |    2 ++
 gio/src/pollableoutputstream.hg |    2 ++
 2 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/gio/src/pollableinputstream.hg b/gio/src/pollableinputstream.hg
index b1c3178..a5dcddf 100644
--- a/gio/src/pollableinputstream.hg
+++ b/gio/src/pollableinputstream.hg
@@ -33,6 +33,8 @@ class Cancellable;
 //TODO: Instead derive from InputStream, when we can break ABI,
 //because the GPollableInputStream interface requires the GInputStream interface.
 //LoadableIcon does a similar thing correctly, for instance.
+// However, GInputStream is an actuall class, deriving from GObject,
+// but GPollableInputStream is a GInterface, that "requires" GInputStream.
 
 /** PollableInputStream - Interface for pollable input streams.
  * PollableInputStream is implemented by InputStreams that can be polled for
diff --git a/gio/src/pollableoutputstream.hg b/gio/src/pollableoutputstream.hg
index c735fc6..2ab20cb 100644
--- a/gio/src/pollableoutputstream.hg
+++ b/gio/src/pollableoutputstream.hg
@@ -33,6 +33,8 @@ class Cancellable;
 //TODO: Instead derive from OutputStream, when we can break ABI,
 //because the GPollableOutputStream interface requires the GOutputStream interface.
 //LoadableIcon does a similar thing correctly, for instance.
+// However, GOutputStream is an actual class, deriving from GObject,
+// but GPollableOutputStream is a GInterface, that "requires" GOutputStream.
 
 /** PollableOutputStream - Interface for pollable output streams.
  * PollableOutputStream is implemented by OutputStreams that can be polled for