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.

src/OpenFOAM/db/IOobject/IOobject.C

@@ -61,7 +61,7 @@ bool Foam::IOobject::IOobject::fileNameComponents
     name.clear();
 
     // called with directory
-    if (::Foam::isDir(path))
+    if (!isDir(path))
     {
         WarningIn("IOobject::fileNameComponents(const fileName&, ...)")
             << " called with directory: " << path << "\n";