Documentation: do not assume that n > 1 in <rev>~$n
Documentation: do not assume that n > 1 in <rev>~$n

We explained <rev>~<n> as <n>th generation grand-parent, but a reader got
confused by the "grand-" part when <n> is 1.

Reword it with "ancestor"; with the "generation" and "following only the
first parents" around there, what we try to describe should be clear
enough now.

Noticed-by: Luke Diamand <6b3799be4300e44489a08090123f3842e6419da5@diamand.org>
Helped-by: Thomas Rast <18f23ef7096473d837b7404952f13710423b8b63@inf.ethz.ch>
Helped-by: Andreas Ericsson <1eabdaf488b3a3682bbca94c5f468f065cdfaf13@op5.se>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git