subversion: security bump to version 1.7.18

Fixes:

CVE-2014-0032 - mod_dav_svn is vunerable to a remotely triggerable
segfault DoS vulnerability when SVNListParentPath is on.

CVE-2014-3522 - Serf RA layer does not correctly validate certificates
with wildcards in them for HTTPS.

CVE-2014-3528 - Credentials cached with Subversion may be sent to the
wrong server.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>