Fixed an issue with the EXIF IFD tags and minor modifications

There was a bug with the EXIF IFD pointer because if its tag type was IFD (type = 13, added in the Tech. Note TIFF Specification Supplement ). The bug has been fixed by adding the IFD_POINTER bit inside the EXIFIFDPointer bitmask. A new related test-class called TIFFMetadataTest has been added.