Have QPDFObjectHandle notice when replaceObject was called

This results in a performance penalty of 1% to 2% when replaceObject
and swapObjects are never called and a somewhat larger penalty if they
are called, but it's worth it to avoid very confusing behavior as
discussed in depth in qpdf#507.

1 files changed, 7 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index e7af70d4..7deada34 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2021-02-25  Jay Berkenbilt  <ejb@ql.org>
+
+	* Bug fix/behavior change: when QPDF::replaceObject or
+	QPDF::swapObjects is called, existing QPDFObjectHandle instances
+	will now notice the change. This removes a long-standing source of
+	bugs and confusing behavior.
+
 2021-02-23  Jay Berkenbilt  <ejb@ql.org>
 
 	* The test for the input and output files being the same wasn't