selection chemistry: implement z-stack order

Bug #1395452

"raise and lower objects" used to stack objects above/below the next overlapping object,
which makes it impossible to change the z-order of objects that don't overlap.

Fixes also the object manager panel

Conflicts:
	src/selection-chemistry.cpp
	src/selection-chemistry.h
	src/sp-item.cpp

(bzr r15698.1.7)

1 files changed, 6 insertions, 2 deletions

diff --git a/src/sp-item.cpp b/src/sp-item.cpp
index e2f678957..368f8896c 100644
--- a/src/sp-item.cpp
+++ b/src/sp-item.cpp
@@ -306,15 +306,17 @@ void SPItem::raiseToTop() {
     }
 }
 
-void SPItem::raiseOne() {
+bool SPItem::raiseOne() {
     auto next_higher = std::find_if(++parent->children.iterator_to(*this), parent->children.end(), &is_item);
     if (next_higher != parent->children.end()) {
         Inkscape::XML::Node *ref = next_higher->getRepr();
         getRepr()->parent()->changeOrder(getRepr(), ref);
+        return true;
     }
+    return false;
 }
 
-void SPItem::lowerOne() {
+bool SPItem::lowerOne() {
     using Inkscape::Algorithms::find_last_if;
 
     auto next_lower = find_last_if(parent->children.begin(), parent->children.iterator_to(*this), &is_item);
@@ -325,7 +327,9 @@ void SPItem::lowerOne() {
             ref = next_lower->getRepr();
         }
         getRepr()->parent()->changeOrder(getRepr(), ref);
+        return true;
     }
+    return false;
 }
 
 void SPItem::lowerToBottom() {