Use pkgsrc's patch to fix build

The subversion port was upgraded to version 1.9. devel/kdesdk4-kioslaves fails
to build against it now.

pkgsrc has a patch that fixes this issue in
${CVSROOT}/devel/kdesdk-kioslaves/patches/patch-svn_svn.cpp
of their repository. Add this patch.

Approved by: rakuco (mentor)
Obtained from: pkgsrc
Differential Revision: https://reviews.freebsd.org/D4002