Add KDE 5 support to the KWallet auth provider. The --with-kwallet option now looks for KDE 5 before looking for KDE 4. Both 4 and 5 use the same underlying storage and so passwords written by one can be read by the other.
* build/ac-macros/kwallet.m4 (SVN_LIB_KWALLET): Detect KDE 4 and 5.
* build/ac-macros/compiler.m4 (SVN_CXX_MODE_SETUP11): New, set -std=c++11.
* subversion/libsvn_auth_kwallet/kwallet.cpp (kwallet_password_get, kwallet_password_set): Support KDE 4 and 5.