When not looking for a regression during a bisect but for a fix or a
change in another given property, it can be confusing to use 'good'
and 'bad'.

This patch introduce `git bisect new` and `git bisect old` as an
alternative to 'bad' and good': the commits which have a certain
property must be marked as `new` and the ones which do not as `old`.

The output will be the first commit after the change in the property.
During a new/old bisect session you cannot use bad/good commands and
vice-versa.

Some commands are still not available for old/new:
     * git rev-list --bisect does not treat the revs/bisect/new and
       revs/bisect/old-SHA1 files.

Old discussions:
	- http://thread.gmane.org/gmane.comp.version-control.git/86063
		introduced bisect fix unfixed to find fix.
	- http://thread.gmane.org/gmane.comp.version-control.git/182398
		discussion around bisect yes/no or old/new.
	- http://thread.gmane.org/gmane.comp.version-control.git/199758
		last discussion and reviews
New discussions:
	- http://thread.gmane.org/gmane.comp.version-control.git/271320
		( v2 1/7-4/7 )
	- http://comments.gmane.org/gmane.comp.version-control.git/271343
		( v2 5/7-7/7 )
Signed-off-by: NAntoine Delaite <antoine.delaite@ensimag.grenoble-inp.fr>
Signed-off-by: NLouis Stuber <stuberl@ensimag.grenoble-inp.fr>
Signed-off-by: NValentin Duperray <Valentin.Duperray@ensimag.imag.fr>
Signed-off-by: NFranck Jonas <Franck.Jonas@ensimag.imag.fr>
Signed-off-by: NLucien Kong <Lucien.Kong@ensimag.imag.fr>
Signed-off-by: NThomas Nguy <Thomas.Nguy@ensimag.imag.fr>
Signed-off-by: NHuynh Khoi Nguyen Nguyen <Huynh-Khoi-Nguyen.Nguyen@ensimag.imag.fr>
Signed-off-by: NMatthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>