[$] Moving Git past SHA-1

The SHA-1 hashalgorithm has been known for at least a decade to be weak; while no generated hash collisions had been reported, it was assumedthat this would happen before too long. On February 23, Google announcedthat it had succeeded at this task. While the technique used iscomputationally expensive, this event has clarified what most developershave known for some time: it is time to move away from SHA-1. While themigration has essentially been completed in some areas (SSL certificates,for example), there are still important places where it is heavily used,including at the core of the Git source-code management system.Unsurprisingly, the long-simmering discussion in the Git community onmoving away from SHA-1 is now at a full boil.