Karsten Blees authored Nov 14, 2013 and Junio C Hamano committed Nov 18, 2013

The find_exact_renames function currently only uses the hash table for
grouping, i.e.:

1. add sources
2. add destinations
3. iterate all buckets, per bucket:
4. split sources from destinations
5. iterate destinations, per destination:
6. iterate sources to find best match

This can be simplified by utilizing the lookup functionality of the hash
table, i.e.:

1. add sources
2. iterate destinations, per destination:
3. lookup sources matching the current destination
4. iterate sources to find best match

This saves several iterations and file_similarity allocations for the
destinations.

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>