+ default HEAD hash is SHA-1
+
+ Effects:
+
+ Existing projects will not switch to SHA-512 willy-nilly.
+ New projects will still use SHA-1.
+
+ Incompatible new-style commits cannot be pushed without server
+ admin effort (or until future upgrade).
+
+ So all old git clients still work.
+
+Y4: SHA-512 by default for new projects.
+ Conversion enabled for existing projects.
+ Old git software is now pretty firmly deprecated.
+
+ Default configuration change:
+
+ When creating a new bare tree, a configuration dropping is left
+ (in `config') which specifies that SHA-1 is OBSOLESCENT
+
+ Default status for SHA-512 is FORBIDDEN if SHA-1 is ENABLED,
+ or ENABLED if SHA-1 is OBSOLESCENT.
+
+ default HEAD hash is newest ENABLED hash.
+
+ Effects:
+
+ When creating a new working tree, it starts using SHA-512.
+ A new server tree will accept SHA-512.
+
+ Existing server trees do not yet accept SHA-512. They publish
+ their SHA-1 hashes, so clients make commits with SHA-1.
+
+ To convert a project, an administrator would set SHA-1 to
+ OBSOLESCENT on the server. All clones after that will have HEAD
+ with a SHA-512 name. Fetches and pulls will update to SHA-512
+ names.
+
+will , and push one SHA-512 commit to
+ mainline.
+
+
+
+ Default configuration change:
+
+ Effects:
+
+ When creating a new tree with working tree with git init (ie, no
+ HEAD), the default HEAD hash is set to SHA-512 (because SHA-1 is
+ OBSOLESCENT in a new tree and therefore SHA-512 is the only
+ ENABLED hash and is the default).
+
+ Newly minted server trees accept SHA-512.
+
+
+ start using SHA-512 by default.
+
+Y6: Existing projects start being converted infectiously.
+ It is hard to stop this happening.
+ Old git software is firmly stuffed.
+
+ Default configuration change:
+ SHA-1 is OBSOLESCENT
+ (default for SHA-512, and HEAD hash, computed as in Y4)
+
+ Result is that by default all software
+
+ (Projects which do not want to convert need to set SHA-1 to
+ ENABLED, explicitly, on their