lib: New data structure - smap.

A smap is a string to string hash map.  It has a cleaner interface
than shash's which were traditionally used for the same purpose.
This patch implements the data structure, and changes netdev and
its providers to use it.

Signed-off-by: Ethan Jackson <ethan@nicira.com>

utilities/ovs-vsctl.c

@@ -3936,7 +3936,7 @@ do_vsctl(const char *args, struct vsctl_command *commands, size_t n_commands,
         table_destroy(c->table);
         free(c->table);
 
-        smap_destroy(&c->options);
+        shash_destroy_free_data(&c->options);
     }
     free(commands);