ENH: add infoSwitch to control reporting of slaves/roots (closes #531)

- With many processors, the number of entries becomes quite large.

  New controlDict InfoSwitches: "writeSlaves", "writeRoots".

etc/controlDict

@@ -35,11 +35,21 @@ Documentation
 
 InfoSwitches
 {
+    // The default ASCII write precision
     writePrecision  6;
+
+    // Enable job info
     writeJobInfo    0;
+
     writeDictionaries 0;
     writeOptionalEntries 0;
 
+    // Report list of slaves/pids used (parallel)
+    writeSlaves     1;
+
+    // Report list of roots used (parallel)
+    writeRoots      1;
+
     // Allow profiling
     allowProfiling  1;
 
@@ -88,10 +98,11 @@ OptimisationSwitches
     setNaN          0;
 
     // Force dumping (at next timestep) upon signal (-1 to disable)
-    writeNowSignal              -1; // 10;
+    // See 'kill -l' for signal numbers (eg, 10=USR1, 12=USR2)
+    writeNowSignal          -1; // 10;
 
     // Force dumping (at next timestep) upon signal (-1 to disable) and exit
-    stopAtWriteNowSignal        -1;
+    stopAtWriteNowSignal    -1;
 }
 
 /* Can specify fallback profiling settings

src/OpenFOAM/global/argList/argList.C

@@ -885,10 +885,9 @@ void Foam::argList::parse
         case_ = globalCase_;
     }
 
-
     stringList slaveProcs;
 
-    // Collect slave machine/pid
+    // Collect slave machine/pid, and check that the build is identical
     if (parRunControl_.parRun())
     {
         if (Pstream::master())
@@ -934,6 +933,18 @@ void Foam::argList::parse
         }
     }
 
+    // Keep or discard slave and root information for reporting:
+    if (Pstream::master() && parRunControl_.parRun())
+    {
+        if (!debug::infoSwitch("writeSlaves", 1))
+        {
+            slaveProcs.clear();
+        }
+        if (!debug::infoSwitch("writeRoots", 1))
+        {
+            roots.clear();
+        }
+    }
 
     if (Pstream::master() && bannerEnabled_)
     {
@@ -942,7 +953,10 @@ void Foam::argList::parse
 
         if (parRunControl_.parRun())
         {
-            Info<< "Slaves : " << slaveProcs << nl;
+            if (slaveProcs.size())
+            {
+                Info<< "Slaves : " << slaveProcs << nl;
+            }
             if (roots.size())
             {
                 Info<< "Roots  : " << roots << nl;