Update to 1.9.20

Changelog:
Version 1.6.20
(04 Jan 2013, from /branches/1.6.x)
http://svn.apache.org/repos/asf/subversion/tags/1.6.20

User-visible changes
  - Client- and server-side bugfixes:
    * Fix typos in pt_BR, es and zh_TW translations (r1402417)

  - Server-side bugfixes:
    * add Vary: header to GET responses to improve cacheability (r1390653)
    * fix fs_fs to cleanup after failed rep transmission (r1403964, et al)
    * fix an assert with SVNAutoVersioning in mod_dav_svn (issue #4231)

Version 1.6.19
(10 Sep 2012, from /branches/1.6.x)
http://svn.apache.org/repos/asf/subversion/tags/1.6.19

  - Client-side bugfixes:
    * handle missing svn:date reported by svnserve gracefully (r1306111)

  - Server-side bugfixes:
    * fix possible server hang if a hook script fails to start (r1330410)
    * fix write-through proxy commit regression introduced in 1.6.17 (r1088602)
    * partial sync drops properties when converting to adds (issue #4184)

  - Developer-visible changes:
    * fix the testsuite to avoid FAILs on APR hash order (r1230714, et al)

Version 1.6.18
(29 Mar 2012, from /branches/1.6.x)
http://svn.apache.org/repos/asf/subversion/tags/1.6.18

  User-visible changes:
    * reject invalid svn:mergeinfo at commit time over DAV (issue #3953)
    * fix reintegrate merge regression introduced in 1.6.13 (issue #3957)
    * make the stderr output of the post-commit hook XML-safe (r893478)
    * fix a rare source of FSFS corruption (r1240752)
    * plug a memory leak in the bdb backend (r1205726)
    * server-side performance fix for "log -g" (r1152282)
    * fix description of svndumpfilter's --targets option (r1151911)
    * fix datastream corruption during resumed transfer in ra_serf (r1154733)
    * fix a crash in ra_svn SASL authentication (r1166555, -678)
    * fix potential corruption on 32-bit FSFS with large files (r1230212)
    * make website links point to subversion.apache.org (r896893, -901, r915036)
    * fix non-fatal FSFS corruption bug with concurrent commits (issue #4129)

  Developer-visible changes:
    * fix sqlite distfile retrieval in get-deps.sh (r1134734)
    * fix swig-py memory leak (r1235264, -296, -302, -736)
    * allow passing --with-jdk to gen-make.py on Windows (r966167)

(ryoon)