ENH: use main constant/triSurface directory for sampling surfaces (closes #704)

- these were previously taken from region-local directories
  (eg, constant/region/triSurface), but this becomes difficult to
  manage when there are many files and regions.

src/sampling/sampledSurface/sampledTriSurfaceMesh/sampledTriSurfaceMesh.C

@@ -647,7 +647,7 @@ Foam::sampledTriSurfaceMesh::sampledTriSurfaceMesh
             surfaceName,
             mesh.time().constant(), // instance
             "triSurface",           // local
-            mesh,                   // registry
+            mesh.time(),            // registry
             IOobject::MUST_READ,
             IOobject::NO_WRITE,
             false
@@ -679,7 +679,7 @@ Foam::sampledTriSurfaceMesh::sampledTriSurfaceMesh
             dict.lookup("surface"),
             mesh.time().constant(), // instance
             "triSurface",           // local
-            mesh,                   // registry
+            mesh.time(),            // registry
             IOobject::MUST_READ,
             IOobject::NO_WRITE,
             false
@@ -712,7 +712,7 @@ Foam::sampledTriSurfaceMesh::sampledTriSurfaceMesh
             name,
             mesh.time().constant(), // instance
             "triSurface",           // local
-            mesh,                   // registry
+            mesh.time(),            // registry
             IOobject::NO_READ,
             IOobject::NO_WRITE,
             false

src/sampling/surface/triSurfaceMesh/discreteSurface.C

@@ -642,7 +642,7 @@ Foam::discreteSurface::discreteSurface
             surfaceName,
             mesh.time().constant(), // instance
             "triSurface",           // local
-            mesh,                   // registry
+            mesh.time(),            // registry
             IOobject::MUST_READ,
             IOobject::NO_WRITE,
             false
@@ -680,7 +680,7 @@ Foam::discreteSurface::discreteSurface
             dict.lookup("surface"),
             mesh.time().constant(), // instance
             "triSurface",           // local
-            mesh,                   // registry
+            mesh.time(),            // registry
             IOobject::MUST_READ,
             IOobject::NO_WRITE,
             false
@@ -716,7 +716,7 @@ Foam::discreteSurface::discreteSurface
             name,
             mesh.time().constant(), // instance
             "triSurface",           // local
-            mesh,                   // registry
+            mesh.time(),            // registry
             IOobject::NO_READ,
             IOobject::NO_WRITE,
             false