Fix for bug #90499: Can't delete selection if end of selection contains "<br>\n"

Modified nsHTMLEditRules::WillDeleteSelection() so that it uses
an nsAutoTxnsConserveSelection auto-variable to prevent the
call to nsWSRunObject::PrepareToDeleteRange() from changing
the selection.

r=brade@netscape.com  sr=waterson@netscape.com

editor/base/nsHTMLEditRules.cpp

@@ -1847,6 +1847,7 @@ nsHTMLEditRules::WillDeleteSelection(nsISelection *aSelection,
   // adjust surrounding whitespace in preperation to delete selection
   if (!bPlaintext)
   {
+    nsAutoTxnsConserveSelection dontSpazMySelection(mHTMLEditor);
     res = nsWSRunObject::PrepareToDeleteRange(mHTMLEditor,
                                             address_of(startNode), &startOffset, 
                                             address_of(endNode), &endOffset);

editor/libeditor/html/nsHTMLEditRules.cpp

@@ -1847,6 +1847,7 @@ nsHTMLEditRules::WillDeleteSelection(nsISelection *aSelection,
   // adjust surrounding whitespace in preperation to delete selection
   if (!bPlaintext)
   {
+    nsAutoTxnsConserveSelection dontSpazMySelection(mHTMLEditor);
     res = nsWSRunObject::PrepareToDeleteRange(mHTMLEditor,
                                             address_of(startNode), &startOffset, 
                                             address_of(endNode), &endOffset);