rename Foam::dotFoam() -> Foam::findEtcFile() with an optional 'mandatory' argument

- if mandatory is true, findEtcFile() will abort with a message (via cerr).
  This allows a non-existent file to be caught at the lowest level and avoid
  error handling in IFstream, which might not be initialized at that stage.

src/OSspecific/Unix/Unix.C

@@ -211,7 +211,7 @@ bool Foam::chDir(const fileName& dir)
 }
 
 
-Foam::fileName Foam::dotFoam(const fileName& name)
+Foam::fileName Foam::findEtcFile(const fileName& name, bool mandatory)
 {
     // Search user files:
     // ~~~~~~~~~~~~~~~~~~
@@ -268,6 +268,15 @@ Foam::fileName Foam::dotFoam(const fileName& name)
     }
 
     // Not found
+    // abort if the file is mandatory, otherwise return null
+    if (mandatory)
+    {
+        cerr<< "--> FOAM FATAL ERROR in Foam::findEtcFile() :"
+               " could not find mandatory file\n    '"
+            << name.c_str() << "'\n\n" << std::endl;
+        ::exit(1);
+    }
+
     return fileName::null;
 }