Merge branch 'jk/rev-list-stdin-noop-is-ok'

"git rev-list --stdin </dev/null" used to be an error; it now shows
no output without an error.  "git rev-list --stdin --default HEAD"
still falls back to the given default when nothing is given on the
standard input.

* jk/rev-list-stdin-noop-is-ok:
rev-list: make empty --stdin not an error

diff --cc builtin/rev-list.c
Simple merge

diff --cc revision.c
Simple merge

diff --cc revision.h
Simple merge