Introduce another scratch pool in the server-side log code, reducing the
the resident memory size of an 'svn log -v' process from 407M to 317M while
showing r11708 of ruby's Subversion repository via ra_local (on OpenBSD).
Ruby's r11708 sets svn:eol-style on 123934 files...

* subversion/libsvn_fs_fs/low_level.c
  (read_change): Switch to dual-pool parameters, and use a scratch pool for
   lines read from the revision file and a result_pool for returned data.
  (svn_fs_fs__read_changes): Use an iterpool while looping over changes
   and pass it as a scratch pool to read_change().
  (svn_fs_fs__read_changes_incrementally): Same, except this was already
   passing an iterpool pool as the result pool.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1604700 13f79535-47bb-0310-9956-ffa450edef68