hide repating property name

[jstavel]

There are a lot of rows in comparison siginificant properties list.
Application should write just first occurence of SP.
Other occurences of SP name would be left empty.

see text output:
http://differ.readthedocs.org/en/latest/_downloads/cmdline.txt

e.g.:

MIME type exiftool image/jpeg
exiv2 image/jpeg
fits image/jpeg
jhove image/jpeg

So If some text is repeating, next occurrence of the text is hidden.

It helps text to be readable a lot.