reachable.hon commit docs: clarify what git-rebase's "-p" / "--preserve-merges" does (d50d31e)
   1#ifndef REACHEABLE_H
   2#define REACHEABLE_H
   3
   4struct progress;
   5extern void mark_reachable_objects(struct rev_info *revs, int mark_reflog, struct progress *);
   6
   7#endif