document the convention used for Euler angles (XY'Z'')

in the Placement dialog and the docstrings of the Rotation python class.
fixes #2007

src/Base/RotationPy.xml

@@ -21,7 +21,7 @@
 				-- a Rotation object
 				-- a Vector (axis) and a float (angle)
 				-- two Vectors (rotation from/to vector)
-				-- three floats (Euler angles) as yaw-pitch-roll
+				-- three floats (Euler angles) as yaw-pitch-roll in XY'Z'' convention
 				-- four floats (Quaternion) where the quaternion is specified as:
 				   q=xi+yj+zk+w, i.e. the last parameter is the real part
 			</UserDocu>
@@ -55,6 +55,7 @@
 				<UserDocu>
 					toEuler(Vector) -> list
 					Get the Euler angles of this rotation
+					as yaw-pitch-roll in XY'Z'' convention
 				</UserDocu>
 			</Documentation>
 		</Methode>

src/Gui/Placement.cpp

@@ -430,7 +430,7 @@ Base::Placement Placement::getPlacementData() const
         Base::Vector3d dir = getDirection();
         rot.setValue(Base::Vector3d(dir.x,dir.y,dir.z),Base::toRadians(ui->angle->value().getValue()));
     }
-    else if (index == 1) {
+    else if (index == 1) { // Euler angles (XY'Z'')
         rot.setYawPitchRoll(
             ui->yawAngle->value().getValue(),
             ui->pitchAngle->value().getValue(),

src/Gui/Placement.ui

@@ -338,7 +338,7 @@
         </item>
         <item>
          <property name="text">
-          <string>Euler angles</string>
+          <string>Euler angles (XY'Z'')</string>
          </property>
         </item>
        </widget>