ra_dav client memory use during update

The memory use of the client during update over ra_dav appears to
depend on the number of files updated in a directory. If hundreds of
files change then the client uses hundreds of MB of memory. This only
occurs over ra_dav, not over ra_local.

Run this command

tools/dev/stress.pl -c -N1 -D1 -F201 -n1 -x200 -s1

that creates a repository and a working copy in the current directory.
The repository contains 200 files in a single directory, and there are
two revisions, in the first the files get created and in the second
they get updated. The working copy uses ra_local.

Now checkout a new working copy from the repository over ra_dav.
Updating the new working copy to the other revision causes the client
to use hundreds of MB.

Repeat the exercise using

tools/dev/stress.pl -c -N2 -D40 -F5 -n1 -x200 -s1

which puts 5 files in each of 40 directories. This time the update
over ra_dav uses less than 20 MB.

cmpilato thinks it may have been the recent editor conversion, which
sounds plausible.