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/IOstreams/Fstreams/OFstream.C

@@ -57,7 +57,8 @@ Foam::OFstreamAllocator::OFstreamAllocator
 
     if (compression == IOstream::COMPRESSED)
     {
-        if (isFile(pathname))
+        // get identically named uncompressed version out of the way
+        if (isFile(pathname, false))
         {
             rm(pathname);
         }
@@ -66,7 +67,8 @@ Foam::OFstreamAllocator::OFstreamAllocator
     }
     else
     {
-        if (isFile(pathname + ".gz"))
+        // get identically named compressed version out of the way
+        if (isFile(pathname + ".gz", false))
         {
             rm(pathname + ".gz");
         }