roots: split constructor into separate start method

This allows us to use the fd cache and inode resolve functions
without starting crawler threads.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

src/bees-context.cc

@@ -987,7 +987,7 @@ BeesContext::start()
 	hash_table();
 
 	// Kick off the crawlers
-	roots();
+	roots()->start();
 }
 
 void