It seems necessary to control destruction ordering to avoid a
segfault with SVN 1.9.5 when using "git svn branch".  I've also
reported the problem against libsvn-perl to Debian [Bug #888791],
but releasing the SVN::Client instance can be beneficial anyways to
save memory.

ref: https://bugs.debian.org/888791Tested-by: NTodd Zullinger <tmz@pobox.com>
Reported-by: Nbrian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: NEric Wong <e@80x24.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>