Fix bad link ref. when system leveldb exists v2.

Take II, folks.

This commit fixes a link-time issue that comes about when an
incompatible system-level leveldb is already installed. The problem is
that leveldb isn't listed as a dependency, so link-time -lleveldbs
aren't preceded by -L{prefix to the leveldb I actually want}/lib, so
when a potentially incompatible system-level leveldb exists, then bad
things happen.

@brobey you might be interested in this.

Makefile.am

@@ -71,6 +71,7 @@ if BUILD_LEVELDB
 lib_libsdskv_server_la_SOURCES += src/datastore/leveldb_datastore.cc
 endif
 
+lib_libsdskv_server_la_LIBADD = ${SERVER_LIBS}
 
 include_HEADERS = include/sdskv-client.h \
 		  include/sdskv-server.h \