git hooks update

[Joseph Myers]

I've updated the gcc-reposurgeon-8 test repository 
(git+ssh://gcc.gnu.org/home/gccadmin/gcc-reposurgeon-8.git) to use the 
same copy of the git hooks as used by binutils-gdb, glibc and other 
repositories on sourceware.

All the features from local hook changes are now handled, with this new 
version, through new configuration variables (in project.config on 
refs/meta/config) and three new scripts referenced in project.config: 
commit_checker, commit_email_formatter and update_hook in 
~gccadmin/hooks-bin.  This version also has various upstream improvements.  
In particular, the email-new-commits-only variable means that no commit 
emails should be sent for commits added to refs under refs/heads/devel/, 
refs/users/ or refs/vendors/ that were already in the repository (so with 
the new hooks, merges to and rebases of such branches should not generate 
floods of commit emails).

Please test whether the hooks are working as expected with the expected 
checks properly implemented in gcc-reposurgeon-8.  If they're working OK, 
we can switch over in the production repository by changing the 
/git/gcc.git/hooks symlink to point to 
/sourceware/projects/src-home/git-hooks/hooks instead of 
/home/gccadmin/git-hooks/hooks, and uncommenting the 
allow-non-fast-forward settings in project.config in the production 
repository.

Once we've switched over, we'll be using a copy of the hooks that is 
shared by other projects, rather than a GCC-specific copy, and so should 
avoid making local changes there.

-- 
Joseph S. Myers
joseph@codesourcery.com