busybox:
 * rename busybox.rebuld-subopts.mk back to busybox.rebuild-subopts.mk.in
 * fixes the file is included twice (from source:trunk/Makefile#L207 and from busybox.mk), the 1st include caused additional variable _REBUILD_SUBOPTS (without pkg-prefix) to be defined
 * fixes "check changes" considers busybox.rebuild-subopts.mk.in again as its name matches expected pattern (source:trunk/make/Makefile.in#L751)
 * sort REBUILD_SUBOPTS alphabetically
 * refs #1786, refs r9890


git-svn-id: file:///var/svn/freetz/trunk@9899 149334a1-2f27-0410-a3b9-fc62619ac1e6