patchgit-svn: disable _rev_list memoization

This memoization appears unneeded as the check_cherry_pick2 cache is in front of it does enough.

With this change applied, importing from local svn+ssh and http copies of the R repo[1] takes only 2:00 (2 hours) on my system and the git-svn process never uses more than 60MB RSS on my x86-64 GNU/Linux system[2]. This 60M measurement is only for the git-svn Perl process itself and does not include memory used by git subprocesses accessing large packs (subprocess memory usage _is_ measured by my time(1) tool).

Before this change, an import took longer (2:20) on svn+ssh:// but git-svn used around 240MB during the imports. Worse yet, git-svn ballooned to over 400M when writing out the cache to the filesystem.

I also tried removing memoization for `has_no_changes', too, but a local copy of the R repository(*) was not close to finishing within 10 hours on my system.

[1] http://svn.r-project.org/R [2] file:// repos causes libsvn to use more memory internally

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Cc: Hin-Tak Leung <htl10@users.sourceforge.net>
---
  This patch is in my "less-memo" branch of bogomips.org/git-svn.git
  Info here:

  (not intended as a pull request for Junio, yet)

  The following changes since commit fbecd99861ea5795aeba46faf2ac7a8c1b70d485:

    Update draft release notes to 2.2 (2014-10-24 15:02:17 -0700)

  are available in the git repository at:

    git://bogomips.org/git-svn.git less-memo

  for you to fetch changes up to 7676aff70973e617c3f58a8633db6d0e3ee99e45:

    git-svn: disable _rev_list memoization (2014-10-27 01:39:39 +0000)

  ----------------------------------------------------------------
  Eric Wong (7):
        git-svn: reduce check_cherry_pick cache overhead
        git-svn: cache only mergeinfo revisions
        git-svn: remove mergeinfo rev caching
        git-svn: reload RA every log-window-size
        git-svn: remove unnecessary DESTROY override
        git-svn: save a little memory as fetch progresses
        git-svn: disable _rev_list memoization

  Jakob Stoklund Olesen (2):
        git-svn: only look at the new parts of svn:mergeinfo
        git-svn: only look at the root path for svn:mergeinfo

  Sveinung Kvilhaugsvik (1):
        git-svn.txt: advertise pushurl with dcommit

   Documentation/git-svn.txt |   4 ++
   perl/Git/SVN.pm           | 121 +++++++++++++++++++++++++++++-----------------
   perl/Git/SVN/Ra.pm        |  27 ++++++-----
   3 files changed, 94 insertions(+), 58 deletions(-)

 perl/Git/SVN.pm | 10 ----------
 1 file changed, 10 deletions(-)