Add xref Makefile target.

Conflicts:
	rebar.config.script
Ignore riak_object module call for xref check.

It's used in map-reduce function called from riak vm.
Fix xref check when odbc driver is not used.
fix invalid path of jiffy.so on install #309
Clean up rebar script.
Merge branch 'master' of github.com:processone/ejabberd
don't stop on error if jiffy.so symlink exists #309
Merge branch 'master' of github.com:processone/ejabberd
Add tests for mod_vcard_xupdate
Fix race in CSI test case