Fix typos in source comments

Found via `codespell`

src/Mod/Path/PathScripts/PathDressupPathBoundary.py

@@ -110,7 +110,7 @@ class DressupPathBoundary(object):
 
             boundary = obj.Stock.Shape
             cmd = obj.Base.Path.Commands[0] 
-            pos = cmd.Placement.Base # bogus m/c postion to create first edge 
+            pos = cmd.Placement.Base # bogus m/c position to create first edge 
             bogusX = True
             bogusY = True
             commands = [cmd]

src/Mod/Sketcher/Gui/DrawSketchHandler.h

@@ -113,7 +113,7 @@ protected:
     void setCrosshairCursor(const char* svgName);
 
     /**
-     * Returns contraints icons scaled to width.
+     * Returns constraints icons scaled to width.
      **/
     std::vector<QPixmap> suggestedConstraintsPixmaps(
             std::vector<AutoConstraint> &suggestedConstraints);

src/Mod/TechDraw/Gui/MDIViewPage.h

@@ -64,7 +64,7 @@ public:
     void onSelectionChanged(const Gui::SelectionChanges& msg);
     void preSelectionChanged(const QPoint &pos);
 
-    /// QGraphicsScene seletion routines
+    /// QGraphicsScene selection routines
     void selectQGIView(App::DocumentObject *obj, bool state);
     void clearSceneSelection();
     void blockSelection(bool isBlocked);