Merge branch 'jc/read-tree-ignore'

* jc/read-tree-ignore:
  read-tree: document --exclude-per-directory
  Loosen "working file will be lost" check in Porcelain-ish
  read-tree: further loosen "working file will be lost" check.

diff --cc git-merge.sh
Simple merge

diff --cc unpack-trees.c
Simple merge