[git] How to change Git log date formats

Git 2.7 (Q4 2015) will introduce -local as an instruction.
It means that, in addition to:

--date=(relative|local|default|iso|iso-strict|rfc|short|raw)

you will also have:

--date=(default-local|iso-local|iso-strict-local|rfc-local|short-local)

The -local suffix cannot be used with raw or relative. Reference.

You now can ask for any date format using the local timezone. See

See commit add00ba, commit 547ed71 (03 Sep 2015) by Jeff King (peff).
(Merged by Junio C Hamano -- gitster -- in commit 7b09c45, 05 Oct 2015)

In particular, the last from above (commit add00ba) mentions:

date: make "local" orthogonal to date format:

Most of our "--date" modes are about the format of the date: which items we show and in what order.
But "--date=local" is a bit of an oddball. It means "show the date in the normal format, but using the local timezone".
The timezone we use is orthogonal to the actual format, and there is no reason we could not have "localized iso8601", etc.

This patch adds a "local" boolean field to "struct date_mode", and drops the DATE_LOCAL element from the date_mode_type enum (it's now just DATE_NORMAL plus local=1).
The new feature is accessible to users by adding "-local" to any date mode (e.g., "iso-local"), and we retain "local" as an alias for "default-local" for backwards compatibility.