MFC r307003, r307564: makewhatis: make output reproducible

MFC r307003, r307564: makewhatis: make output reproducible

r307003: Instead:

1) provide fts_open() with a comparison function to process directories
   and files in a deterministic order
2) in addition to the existing hash, insert pages into a linked list
   which will be sorted (by virtue of 1)
3) iterate over pages by the list in 2, instead of hash order

Idea from:	des

r307564: makewhatis: avoid skipping another page after one with no mlinks

Submitted by:	Ingo Schwarze

Sponsored by:	The FreeBSD Foundation