ENH: snappyHexMesh: additional parameter for layer truncation

applications/utilities/mesh/generation/snappyHexMesh/snappyHexMeshDict

@@ -310,6 +310,10 @@ addLayersControls
     //  make straight angle.
     featureAngle 60;
 
+    //- At non-patched sides allow mesh to slip if extrusion direction makes
+    //  angle larger than slipFeatureAngle.
+    slipFeatureAngle 30;
+
     //- Maximum number of snapping relaxation iterations. Should stop
     //  before upon reaching a correct mesh.
     nRelaxIter 5;