src/makefile: link boost-filesystem to libdsscore

An attempt to fix http://dsjenkins.cloudapp.net/jenkins/job/dSS/596/console

src/Makefile.inc

@@ -60,6 +60,7 @@ libdsscore_a_CXXFLAGS = \
 			$(EXPAT_CFLAGS) \
 			$(GCOV_CFLAGS) \
 			$(OSSP_UUID_CFLAGS) \
+			$(BOOST_FILESYSTEM_LIB) \
 			$(LIBPROTOBUF_CFLAGS) \
 			$(LIBCOMMCHANNEL_CFLAGS) \
 			$(LIBDSUID_CFLAGS)