Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

 rcommit

 rdiff

 rdiff(Arg1)

 rdiff(Arg1, Arg2)

 rreset

 rsave(Arg1)

 rshow

 apply_command_q(Arg1)

 rdelete(Arg1)

 rlist

 rlist(Arg1)

 rnostats

 rrewind

 rrewind(Arg1)

 rstats

 rundo