objectRegistry fixes

- objectRegistry gets a rename() that also adjusts the dbDir
- cloud reworked to use static variables subInstance and defaultName.
  This avoids writing "lagrangian" everywhere

string fixes
- avoid masking of std::string::replace in string.H
- avoid old strstream in PV3FoamReader

applications/utilities/parallelProcessing/reconstructPar/reconstructPar.C

@@ -277,7 +277,7 @@ int main(int argc, char *argv[])
             (
                 readDir
                 (
-                    databases[procI].timePath()/regionPrefix/"lagrangian",
+                    databases[procI].timePath()/regionPrefix/cloud::subInstance,
                     fileName::DIRECTORY
                 )
             );
@@ -295,7 +295,7 @@ int main(int argc, char *argv[])
                     (
                         procMeshes.meshes()[procI],
                         databases[procI].timeName(),
-                        "lagrangian"/cloudDirs[i]
+                        cloud::subInstance/cloudDirs[i]
                     );
 
                     IOobject* positionsPtr = sprayObjs.lookup("positions");