ENH: provide HashTable::iterator::found() method

- This can be used as a convenient alternative to comparing against end().
  Eg,

    dictionaryConstructorTable::iterator cstrIter =
        dictionaryConstructorTablePtr_->find(methodType);

    if (cstrIter.found())
    {
        ...
    }
  vs.
    if (cstrIter != dictionaryConstructorTablePtr_->end())
    {
        ...
    }

src/OpenFOAM/containers/HashTables/HashTable/HashTableI.H

@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
-     \\/     M anipulation  |
+     \\/     M anipulation  | Copyright (C) 2017 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -257,6 +257,14 @@ Foam::HashTable<T, Key, Hash>::iteratorBase::increment()
 }
 
 
+template<class T, class Key, class Hash>
+inline bool
+Foam::HashTable<T, Key, Hash>::iteratorBase::found() const
+{
+    return entryPtr_;
+}
+
+
 template<class T, class Key, class Hash>
 inline
 const Key& Foam::HashTable<T, Key, Hash>::iteratorBase::key() const