Add a shortcut for adding a reference dimension or angle.

This is equivalent to adding a constraint, then making it a reference.
The benefits are that:
 * it's quicker;
 * it avoids having an over-constrained system, with an associated
   angry red flash and a regeneration delay.
The latter in particular is a very substantial usability improvement.

The reference distance command is useful most of the time,
but the reference angle one is also added for consistency.

src/constraint.cpp

@@ -124,7 +124,8 @@ void Constraint::MenuConstrain(int id) {
 #define gs (SS.GW.gs)
 
     switch(id) {
-        case GraphicsWindow::MNU_DISTANCE_DIA: {
+        case GraphicsWindow::MNU_DISTANCE_DIA:
+        case GraphicsWindow::MNU_REF_DISTANCE: {
             if(gs.points == 2 && gs.n == 2) {
                 c.type = PT_PT_DISTANCE;
                 c.ptA = gs.point[0];
@@ -177,6 +178,10 @@ void Constraint::MenuConstrain(int id) {
                 c.disp.offset = Vector::From(0, 0, 0);
             }
 
+            if(id == GraphicsWindow::MNU_REF_DISTANCE) {
+                c.reference = true;
+            }
+
             c.valA = 0;
             c.ModifyToSatisfy();
             AddConstraint(&c);
@@ -535,7 +540,8 @@ void Constraint::MenuConstrain(int id) {
             Error("Must select a constraint with associated label.");
             return;
 
-        case GraphicsWindow::MNU_ANGLE: {
+        case GraphicsWindow::MNU_ANGLE:
+        case GraphicsWindow::MNU_REF_ANGLE: {
             if(gs.vectors == 2 && gs.n == 2) {
                 c.type = ANGLE;
                 c.entityA = gs.vector[0];
@@ -568,6 +574,11 @@ void Constraint::MenuConstrain(int id) {
                     // no shared point; not clear which intersection to draw
                 }
             }
+
+            if(id == GraphicsWindow::MNU_REF_ANGLE) {
+                c.reference = true;
+            }
+
             c.ModifyToSatisfy();
             AddConstraint(&c);
             break;

src/graphicswin.cpp

@@ -126,7 +126,9 @@ const GraphicsWindow::MenuEntry GraphicsWindow::menu[] = {
 
 { 0, "&Constrain",                  0,                  0,       IN, NULL  },
 { 1, "&Distance / Diameter",        MNU_DISTANCE_DIA,   'D',     IN, mCon  },
+{ 1, "Re&ference Dimension",        MNU_REF_DISTANCE,   S|'D',   IN, mCon  },
 { 1, "A&ngle",                      MNU_ANGLE,          'N',     IN, mCon  },
+{ 1, "Reference An&gle",            MNU_REF_ANGLE,      S|'N',   IN, mCon  },
 { 1, "Other S&upplementary Angle",  MNU_OTHER_ANGLE,    'U',     IN, mCon  },
 { 1, "Toggle R&eference Dim",       MNU_REFERENCE,      'E',     IN, mCon  },
 { 1, NULL,                          0,                  0,       IN, NULL  },

src/ui.h

@@ -396,7 +396,9 @@ public:
         MNU_GROUP_RECENT,
         // Constrain
         MNU_DISTANCE_DIA,
+        MNU_REF_DISTANCE,
         MNU_ANGLE,
+        MNU_REF_ANGLE,
         MNU_OTHER_ANGLE,
         MNU_REFERENCE,
         MNU_EQUAL,