fix package/symlinks target, will call scripts/feeds update / install

introduce new package/symlinks-install and package/symlinks-clean targets
- package/symlink-install will re-create the index files and the symlinks for all ./feeds (no update from repositories is performed)
- package/symlink-clean will delete all installed symlinks (keeping the ./feeds untouched)



git-svn-id: svn://svn.openwrt.org/openwrt/trunk@10634 3c298f89-4303-0410-b956-a3cf2f4a3e73