rev-parse: respect core.hooksPath in --git-path

rev-parse: respect core.hooksPath in --git-path

The idea of the --git-path option is not only to avoid having to
prefix paths with the output of --git-dir all the time, but also to
respect overrides for specific common paths inside the .git directory
(e.g. `git rev-parse --git-path objects` will report the value of the
environment variable GIT_OBJECT_DIRECTORY, if set).

When introducing the core.hooksPath setting, we forgot to adjust
git_path() accordingly. This patch fixes that.

While at it, revert the special-casing of core.hooksPath in
run-command.c, as it is now no longer needed.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>