OSspecific: altered file tests

- removed the previously added fileName type(), isDir(), isFile() methods.

- added optional bool parameter to isFile() function to explicitly
  enable/disable the check for gzip files.

- fixed minor bugginess where the default usage of isFile() would result in
  false positive matches.

- be slightly more stringent and use isDir() and isFile() instead of
  exists() function when we actually know the expected type.

applications/utilities/surface/surfaceMeshConvert/surfaceMeshConvert.C

@@ -122,7 +122,11 @@ int main(int argc, char *argv[])
             (
                 new IOobject
                 (
-                    ( dictPath.isDir() ? dictPath/coordinateSystems::typeName : dictPath ),
+                    (
+                        isDir(dictPath)
+                      ? dictPath/coordinateSystems::typeName
+                      : dictPath
+                    ),
                     runTime,
                     IOobject::MUST_READ,
                     IOobject::NO_WRITE,

applications/utilities/surface/surfaceMeshExport/surfaceMeshExport.C

@@ -119,7 +119,7 @@ int main(int argc, char *argv[])
                 new IOobject
                 (
                     (
-                        dictPath.isDir()
+                        isDir(dictPath)
                       ? dictPath/coordinateSystems::typeName
                       : dictPath
                     ),

applications/utilities/surface/surfaceMeshImport/surfaceMeshImport.C

@@ -133,7 +133,7 @@ int main(int argc, char *argv[])
                 new IOobject
                 (
                     (
-                        dictPath.isDir()
+                        isDir(dictPath)
                       ? dictPath/coordinateSystems::typeName
                       : dictPath
                     ),