ENH: add trapFpe and setNaN optimisationSwitch (issue #517)

- allows configuration without an environment variable.
  For compatibility still respect FOAM_SIGFPE and FOAM_SETNAN
  env-variables

- The env-variables are now treated as true/false switch values.
  Previously there was just a check for env exists or not, but this
  can be fairly fragile for a user's environment.

applications/utilities/parallelProcessing/redistributePar/redistributePar.C

@@ -59,6 +59,7 @@ Usage
 \*---------------------------------------------------------------------------*/
 
 #include "argList.H"
+#include "sigFpe.H"
 #include "Time.H"
 #include "fvMesh.H"
 #include "fvMeshTools.H"
@@ -2277,7 +2278,7 @@ int main(int argc, char *argv[])
     bool newTimes = args.optionFound("newTimes");
 
 
-    if (env("FOAM_SIGFPE"))
+    if (Foam::sigFpe::requested())
     {
         WarningInFunction
             << "Detected floating point exception trapping (FOAM_SIGFPE)."
@@ -2287,7 +2288,6 @@ int main(int argc, char *argv[])
     }
 
 
-
     const HashSet<word> selectedFields(0);
     const HashSet<word> selectedLagrangianFields(0);