patch to show only diffstat in the commit tab

[Vial, Florent]

Hi,

Please find attached a patch that modifies cgit behaviour like following:
The commit tab now only shows the diffstat + diffstat summary, not the full diff anymore. The reason for that is that we have huge tree differences between 2 commits and do not want to overload the web server, only have a summary of the files that were changed in the commit. Only when one clicks on the diff tab, the full diff is displayed.

There were also a lot of refactoring in the cgit_print_*** functions in ui-diff as it was very monolithic.

Cheers,
Florent Vial