Merge branch 'js/git-path-in-subdir'

The "--git-path", "--git-common-dir", and "--shared-index-path"
options of "git rev-parse" did not produce usable output.  They are
now updated to show the path to the correct file, relative to where
the caller is.

* js/git-path-in-subdir:
rev-parse: fix several options when running in a subdirectory
rev-parse tests: add tests executed from a subdirectory

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

diff --cc t/t1500-rev-parse.sh
Simple merge