Proposed new git hook policy: only applies to first-parent, enforces master is
first parent on all merges, enforces issue number (or explicitly stating no
issue number) on all master commits.
Added pattern to permit commits that merge master heads.
Disallow commits that merge local and remote master, in order to maintain
linear history of master.
Added mention of git reset to instructions for remerging/rebasing.
Merge branch 'new-git-hooks' of git.curoverse.com:arvados-dev into new-git-hooks
A few fixes:

a) clarify error message when doing a fast-forward merge rejection

b) reduce number of gratuitous newlines

c) do not test for issue numbers when a fast-forward merge is being
attempted, because that test will complain about every commit, obscuring
the real problem (the fast-forward merge)
Merge branch 'new-git-hooks'

no issue #