* ospf_lsa.h: New flag to the LSA structure for the SPF calculation.

	* ospf_lsa.h: New flag to the LSA structure for the SPF calculation.
	* ospf_lsdb.h: Export ospf_lsdb_clean_stat() function.
	* ospf_spf.h: Add link to the LSA stat structure into vertex.
	* ospf_spf.c: New functions cmp() and update_stat() to manage
	  candidates. Remove ospf_spf_has_vertex(), ospf_vertex_lookup(),
	  ospf_install_candidate() and ospf_spf_register() functions not needed
	  any more. Update ospf_vertex_new(), ospf_spf_next() and
	  ospf_spf_calculate() functions to use pqueue instead of linked list.