randomGenerator: Global flag

A random generator can now be constructed with a global flag. If the
flag is false then the provided seed will be randomised across the
different processes. If the flag is true then the synchronicity of the
generators state will be checked when performing certain operations in
debug mode.

applications/test/parallel/Test-parallel.C

@@ -56,7 +56,7 @@ int main(int argc, char *argv[])
 
     if (true)
     {
-        randomGenerator rndGen(43544*Pstream::myProcNo());
+        randomGenerator rndGen(43544);
 
         // Generate random data.
         List<Tuple2<label, List<scalar>>> complexData(100);