ENH: reduce startup time for ensight conversion (issue #240).

- Less looping when detecting lagrangian clouds and their fields.

- Avoid using Time::setTime() and IOobjectList in tight loops.
  They both kill performance immensely.

ENH: provide a -noLagrangian option to foamToEnsight and foamToEnsightParts
for even more control.

applications/utilities/postProcessing/dataConversion/foamToEnsight/findCloudFields.H

@@ -0,0 +1,93 @@
+// check all time directories for the following:
+
+// The fields for each cloud:
+HashTable<HashTable<word>> cloudFields;
+
+// Identify if lagrangian data exist at any time step.
+if (timeDirs.size() && !noLagrangian)
+{
+    const fileName& baseDir = mesh.time().path();
+    const fileName& cloudPrefix = regionPrefix/cloud::prefix;
+
+    Info<< "Searching for lagrangian ... " << flush;
+
+    forAll(timeDirs, timeI)
+    {
+        const word& timeName = timeDirs[timeI].name();
+
+        // DO NOT USE -->>  runTime.setTime(timeDirs[timeI], timeI);  <<--
+        // It incurs a large overhead when done so frequently.
+
+        fileNameList cloudDirs = readDir
+        (
+            baseDir/timeName/cloudPrefix,
+            fileName::DIRECTORY
+        );
+
+        forAll(cloudDirs, cloudI)
+        {
+            const word& cloudName = cloudDirs[cloudI];
+
+            IOobjectList cloudObjs
+            (
+                mesh,
+                timeName,
+                cloudPrefix/cloudName
+            );
+
+            // clouds always require "positions"
+            if (cloudObjs.found("positions"))
+            {
+                HashTable<HashTable<word>>::iterator cloudIter =
+                    cloudFields.find(cloudName);
+
+                if (cloudIter == cloudFields.end())
+                {
+                    // A newly discovered cloud
+                    cloudFields.insert(cloudName, HashTable<word>());
+                    cloudIter = cloudFields.find(cloudName);
+                }
+
+                forAllConstIter(IOobjectList, cloudObjs, fieldIter)
+                {
+                    const IOobject obj = *fieldIter();
+
+                    // Add field and field type
+                    cloudIter().insert
+                    (
+                        obj.name(),
+                        obj.headerClassName()
+                    );
+                }
+            }
+        }
+    }
+
+    // prune out "positions" again since it gets treated specially
+    forAllIter(HashTable<HashTable<word>>, cloudFields, cloudIter)
+    {
+        cloudIter().erase("positions");
+    }
+
+    if (cloudFields.empty())
+    {
+        Info<< "none detected." << endl;
+    }
+}
+
+
+// sorted list of cloud names
+const wordList cloudNames(cloudFields.sortedToc());
+
+if (cloudNames.size())
+{
+    // complete the echo information
+    Info<< "(";
+    forAll(cloudNames, cloudNo)
+    {
+        Info<< ' ' << cloudNames[cloudNo];
+    }
+    Info<< " ) " << endl;
+}
+
+// ************************************************************************* //