ENH: mutable libs() access in Time and other classes (#1737)

- This reflects the pre-existing coding situation where const_cast was
  used throughout to effect the same.

STYLE: fix private/protected access

- CodedField, codedMixedFvPatchField

src/functionObjects/utilities/codedFunctionObject/codedFunctionObject.C

@@ -96,7 +96,7 @@ void Foam::functionObjects::codedFunctionObject::prepare
 
 Foam::dlLibraryTable& Foam::functionObjects::codedFunctionObject::libs() const
 {
-    return const_cast<Time&>(time_).libs();
+    return time_.libs();
 }
 
 

src/functionObjects/utilities/codedFunctionObject/codedFunctionObject.H

@@ -60,6 +60,7 @@ Usage
         #{
             // Lookup U
             const volVectorField& U = mesh().lookupObject<volVectorField>("U");
+
             // Write
             mag(U)().write();
         #};
@@ -99,7 +100,7 @@ class codedFunctionObject
 {
 protected:
 
-    // Protected data
+    // Protected Data
 
         //- Input dictionary
         dictionary dict_;
@@ -118,7 +119,7 @@ protected:
 
     // Protected Member Functions
 
-        //- Get the loaded dynamic libraries
+        //- Mutable access to the loaded dynamic libraries
         virtual dlLibraryTable& libs() const;
 
         //- Adapt the context for the current object