hook-list.h: add a generated list of hooks, like config-list.h

hook-list.h: add a generated list of hooks, like config-list.h

Resolve a long-standing TODO item in bugreport.c of there being no
centralized listing of hooks, this fixes a bug with the bugreport
listing only knowing about 1/4 of the p4 hooks. It didn't know about
the "reference-transaction" hook either.

We can now make sure this is kept up-to-date, as the hook.c library
will die if asked to find a hook we don't know about yet. The only
(undocumented) exception is the artificial "test-hook" used in our own
test suite. Move some of the tests away from the "does-not-exist"
pseudo-hook, and test for the new behavior.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>