[PATCH 00/19] Untracked cache to speed up "git status"

The last post was five months ago [1]. It's probably time for a resend
in case I'm hit by a bus. Numbers are in 17/19, saving about 40% time
on "git status". Details are in 02/19 and 06/19. Still on the table:

 - index-helper series [2] probably helps save about 10-15% in total
 - watchman support to lower the numbers even more, but not for Windows

I still need to see how watchman can be made on top of this.

[1] http://thread.gmane.org/gmane.comp.version-control.git/248306
[2] http://thread.gmane.org/gmane.comp.version-control.git/254314/focus=254318
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2.1.0.rc0.78.gc0d8480