status: collect per-file data for --porcelain=v2

status: collect per-file data for --porcelain=v2

Collect extra per-file data for porcelain V2 format.

The output of `git status --porcelain` leaves out many
details about the current status that clients might like
to have.  This can force them to be less efficient as they
may need to launch secondary commands (and try to match
the logic within git) to accumulate this extra information.
For example, a GUI IDE might want the file mode to display
the correct icon for a changed item (without having to stat
it afterwards).

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>