STYLE: argList::opt method instead of the longer argList::lookupOrDefault

- also replaced a few instances of readIfPresent with opt<> for
  constant values.

applications/utilities/preProcessing/createExternalCoupledPatchGeometry/createExternalCoupledPatchGeometry.C

@@ -87,7 +87,7 @@ int main(int argc, char *argv[])
     #include "createTime.H"
 
     wordList regionNames(1, fvMesh::defaultRegion);
-    if (!args.readIfPresent("region", regionNames[0]))
+    if (!args.readIfPresent("region", regionNames.first()))
     {
         args.readIfPresent("regions", regionNames);
     }

applications/utilities/preProcessing/foamUpgradeCyclics/foamUpgradeCyclics.C

@@ -431,11 +431,9 @@ int main(int argc, char *argv[])
     }
     const bool enableEntries = args.found("enableFunctionEntries");
 
+    const word regionName = args.opt<word>("region", polyMesh::defaultRegion);
 
-    Foam::word regionName = polyMesh::defaultRegion;
-    args.readIfPresent("region", regionName);
-
-    fileName regionPrefix = "";
+    fileName regionPrefix;
     if (regionName != polyMesh::defaultRegion)
     {
         regionPrefix = regionName;

applications/utilities/preProcessing/mapFields/mapFields.C

@@ -66,7 +66,7 @@ int readNumProcs
                     IOobject::NO_WRITE,
                     false // do not register
                 ),
-                args.lookupOrDefault<fileName>(optionName, "")
+                args.opt<fileName>(optionName, "")
             )
         )
     );