-c -T -R, leaks, malloc checks

[marcin-gryszkalis]

several changes included, unfortunately with old indent (happy to see you switching to 4-spaces).

I don't know is use-case for -c is clear (I'm trying to make an example for man-page, I not commited yet though). I have a script similar to join-duplicates.sh (in perl) but using this -c mode - before I had problems with case with two (or more) groups or hardlinks, eg. 5 file entries, all the same content, hardlinked in groups like:
inode / name:
100 / a.txt
100 / b.txt
200 / c.txt
200 / d.txt
200 / e.txt
and with -p mode duff reported duplicate group of
a.txt
c.txt

• after merge I had
  100 / a.txt
  100 / b.txt
  100 / c.txt
  200 / d.txt
  200 / e.txt

in next run it was not impossible to get from duff -p following list:
d.txt
a.txt
and after merge I had
200 / a.txt
100 / b.txt
100 / c.txt
200 / d.txt
200 / e.txt

and so on... never ending story.
Alternatively I could run duff without -p but it causes reporting all the properly hardlinked groups - not fun either. So -c fixes the case :)

I'll try to update the man page during weekend. Feel free to ask about the changes I made - I'd love to see them in duff ;)