[PATCH] allow svnsync to translate non-UTF-8 log messages to UTF-8 (v. 5)

Attached are version 5 of the patch and log message. The six DUMP
files are the same, and TGZ archives of these files can be downloaded
from Gmane: http://cache.gmane.org//gmane/comp/version-control/subversion/devel/125057-001.bin
and http://cache.gmane.org//gmane/comp/version-control/subversion/devel/125057-002.bin

There was a slight problem with v. 4 of the patch that had something
to do with the concern raised in a message from January 10, 2011:
<http://thread.gmane.org/gmane.comp.version-control.subversion.devel/124731/focus=124967>.
 The issue was that `svnsync` would fail to sync Subversion
repositories containing UTF-8-encoded svn:* props if the
system-default language encoding is not UTF-8. The fix was to not
pass NULL for ENCODING to svn_subst_translate_string2():
https://github.com/dtrebbien/subversion/commit/76b6856818553b9bc62a3c7c7fd2aa084ed1a3e1

Version 5 of the patch also adds a test that `svnsync` can sync
repositories containing UTF-8-encoded svn:* props even if the
system-default language encoding is not UTF-8.