ENH: restart: save/restore cumulative continuity error. See #1172.

src/finiteVolume/cfdTools/general/include/initContinuityErrs.H

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           |
+    \\  /    A nd           | Copyright (C) 2019 OpenCFD Ltd.
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
                             | Copyright (C) 2011 OpenFOAM Foundation
@@ -36,7 +36,20 @@ Description
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-scalar cumulativeContErr = 0;
+uniformDimensionedScalarField cumulativeContErrIO
+(
+    IOobject
+    (
+        "cumulativeContErr",
+        runTime.timeName(),
+        "uniform",
+        mesh,
+        IOobject::READ_IF_PRESENT,
+        IOobject::AUTO_WRITE
+    ),
+    dimensionedScalar(dimless, Zero)
+);
+scalar& cumulativeContErr = cumulativeContErrIO.value();
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //