Add changes file for bug 28938

The fix was in commit 30b84adb5f0b6e56d0fb82c374e3cb44089f64d0.

Signed-off-by: Kris Katterjohn <katterjohn@gmail.com>

changes/bug28938

+  o Minor bugfixes (compilation):
+    - Fix missing headers required for proper detection of
+      OpenBSD.  Fixes bug 28938; bugfix on 0.3.5.1-alpha.
+      Patch from Kris Katterjohn.