STYLE: avoid deprecation warnings for autoPtr set() method

- set() was silently deprecated in favour of reset() FEB-2018
  since the original additional check for overwriting an existing
  pointer was never used. The reset(...) name is more consistent
  with unique_ptr, tmp etc.

  Now emit deprecations for set().

- use direct test for autoPtr, tmp instead of valid() method.
  More consistent with unique_ptr etc.

STYLE: eliminate redundant ptr() use on cloned quantities

src/phaseSystemModels/multiphaseInter/phasesSystem/phaseModel/MultiComponentPhaseModel/MultiComponentPhaseModel.C

@@ -55,14 +55,14 @@ MultiComponentPhaseModel
     species_(),
     inertIndex_(-1)
 {
-    thermoPtr_.set
+    thermoPtr_.reset
     (
         phaseThermo::New
         (
             fluid.mesh(),
             phaseName,
             basicThermo::phasePropertyName(basicThermo::dictName, phaseName)
-        ).ptr()
+        )
     );
 
     if (thermoPtr_->composition().species().empty())