Reintegrate-like merges and diff_ignore_ancestry

Hi,

I was testing recent changes in ra_serf update editor and noticed that
reintegrate-like merges for long living branches are extremely slow.
Client requests server for diff between branches with respect to
ancestry and servers reports no-op txdelta for every file that was
changed in original branch. Then for every such file client retrieves
text and properties.

For example try to reintegrate ev2-export branch back to trunk.

What is the purpose of diff_ignore_ancestry for merges? Can we default
it to FALSE?

I've made simple patch that changes unconditional diff_ignore_ancestry
= FALSE to TRUE in merge_cousins_and_supplement_mergeinfo() call and
everything seems to be working and ALL tests are passing.

-- 
Ivan Zhakov