[glibmm/glibmm-2-60] Glib::Checksum, DateTime, TimeZone: Add TODO comments

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 7e34ef965cc5dd0bdbd261ead838db39bee03f97
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Fri Apr 26 16:28:07 2019 +0200

    Glib::Checksum, DateTime, TimeZone: Add TODO comments
    
    These classes shall have Glib::Value specializations, when we can add API.
    In the master branch, where API and ABI can be changed, they have been
    wrapped as _CLASS_BOXEDTYPE.

 glib/src/checksum.hg | 4 ++++
 glib/src/datetime.hg | 7 ++++---
 glib/src/timezone.hg | 6 +++++-
 3 files changed, 13 insertions(+), 4 deletions(-)
---
diff --git a/glib/src/checksum.hg b/glib/src/checksum.hg
index a4a4d49e..d7b30c4e 100644
--- a/glib/src/checksum.hg
+++ b/glib/src/checksum.hg
@@ -23,6 +23,10 @@ _DEFS(glibmm,glib)
 extern "C" { typedef struct _GChecksum GChecksum; }
 #endif
 
+//TODO: When we can add API, add a Glib::Value specialization, similar to the one in
+// https://mail.gnome.org/archives/gtkmm-list/2019-April/msg00012.html
+//TODO: When we can change API, make Checksum a _CLASS_BOXEDTYPE.
+
 namespace Glib
 {
 
diff --git a/glib/src/datetime.hg b/glib/src/datetime.hg
index ac6e81da..70167046 100644
--- a/glib/src/datetime.hg
+++ b/glib/src/datetime.hg
@@ -26,6 +26,10 @@ _DEFS(glibmm,glib)
 typedef struct _GDateTime GDateTime;
 #endif
 
+//TODO: When we can add API, add a Glib::Value specialization, similar to the one in
+// https://mail.gnome.org/archives/gtkmm-list/2019-April/msg00012.html
+//TODO: When we can change API, make DateTime a _CLASS_BOXEDTYPE.
+
 namespace Glib
 {
 
@@ -49,9 +53,6 @@ using TimeSpan = GTimeSpan;
  * functions can fail due to the date or time going out of range, in which case
  * <tt>0</tt> will be returned.
  *
- * DateTime is reference counted.  When the reference count drops to 0, the
- * resources allocated by the DateTime structure are released.
- *
  * Many parts of the API may produce non-obvious results. As an example, adding
  * two months to January 31st will yield March 31st whereas adding one month
  * and then one month again will yield either March 28th or March 29th. Also
diff --git a/glib/src/timezone.hg b/glib/src/timezone.hg
index afa2f7fd..1c2b0b5a 100644
--- a/glib/src/timezone.hg
+++ b/glib/src/timezone.hg
@@ -25,6 +25,10 @@ _DEFS(glibmm,glib)
 typedef struct _GTimeZone GTimeZone;
 #endif
 
+//TODO: When we can add API, add a Glib::Value specialization, similar to the one in
+// https://mail.gnome.org/archives/gtkmm-list/2019-April/msg00012.html
+//TODO: When we can change API, make TimeZone a _CLASS_BOXEDTYPE.
+
 namespace Glib
 {
 
@@ -32,7 +36,7 @@ _WRAP_ENUM(TimeType, GTimeType, NO_GTYPE)
 
 /** TimeZone - A structure representing a time zone.
  * TimeZone is a structure that represents a time zone, at no particular point
- * in time. It is refcounted and immutable.
+ * in time. It is immutable.
  *
  * A time zone contains a number of intervals. Each interval has an
  * abbreviation to describe it, an offet to UTC and a flag indicating if the