STYLE: HashTable documentation

- explicitly mention the value-initialized status for the operator().
  This means that the following code will properly use an initialized
  zero.

      HashTable<label> regionCount;

      if (...)
         regionCount("region1")++;

      ... and also this;

      if (regionCount("something") > 0)
      {
          ...
      }

  Note that the OpenFOAM HashTable uses operator[] to provide read and
  write access to *existing* entries and will provoke a FatalError if
  the entry does not exist.

  The operator() provides write access to *existing* entries or will
  create the new entry as required.
  The STL hashes use operator[] for this purpose.

applications/test/HashSet/Test-hashSet.C

@@ -28,6 +28,7 @@ Description
 #include "hashedWordList.H"
 #include "HashSet.H"
 #include "Map.H"
+#include "labelPairHashes.H"
 
 using namespace Foam;
 
@@ -122,7 +123,6 @@ int main(int argc, char *argv[])
         << (wordHashSet(setA) | wordHashSet(tableA) | wordHashSet(tableB))
         << nl;
 
-
     labelHashSet setB
     {
         1, 11, 42
@@ -130,6 +130,13 @@ int main(int argc, char *argv[])
 
     Info<< "setB : " << setB << endl;
 
+    labelPair pair(12, 15);
+    setB.set(pair);
+
+    Info<< "setB : " << setB << endl;
+    setB.unset(pair);
+
+
     labelHashSet setC(1);
     setC.insert(2008);
     setC.insert(1984);

applications/test/pTraits/Test-pTraits.C

@@ -51,6 +51,9 @@ void printTraits(const pTraits<T>& p)
 }
 
 
+#pragma GCC diagnostic warning "-Wmaybe-uninitialized"
+#pragma GCC diagnostic warning "-Wuninitialized"
+
 int main()
 {
     printTraits<bool>();
@@ -71,6 +74,12 @@ int main()
 
     printTraits(pTraits<scalar>(3.14159));
 
+    label abc;
+    Info<< "unintialized primitive:"<< abc << endl;
+
+    label def = label();
+    Info<< "intialized primitive:"<< def << endl;
+
     Info<< "End\n" << endl;
 
     return 0;