tests/test-hup.t

branchmap: update cache of 'unserved' filter on new changesets

The `commitctx` and `addchangegroup` methods of repo upgrade branchcache after
completion. This behavior aims to keep the branchcache in sync for read only
process as hgweb. See ee317dbfb9d0 for details.

Since changelog filtering is used, those calls only update the cache for unfiltered repo.
One of no interest for typical read only process like hgweb.

Note: By chance in basic case, `repo.unfiltered() == repo.filtered('unserved')`

This changesets have the "unserved" cache updated instead. I think this is the
only cache that matter for hgweb.

We could imagine updating all possible branchcaches instead but:
- I'm not sure it would have any benefit impact. It may even increase the odd of
  all cache being invalidated.
- This is more complicated change.

So I'm going for updating a single cache only which is already better that
updating a cache nobody cares about.

This changeset have a few expected impact on the testsuite are different cache
are updated.

Test hangup signal in the middle of transaction

  $ "$TESTDIR/hghave" serve fifo || exit 80
  $ hg init
  $ mkfifo p
  $ hg serve --stdio < p 1>out 2>&1 &
  $ P=$!

Do test while holding fifo open

  $ (
  > echo lock
  > echo addchangegroup
  > while [ ! -s .hg/store/journal ]; do sleep 0; done
  > kill -HUP $P
  > ) > p

  $ wait
  $ cat out
  0
  0
  adding changesets
  transaction abort!
  rollback completed
  killed!

  $ echo .hg/* .hg/store/*
  .hg/00changelog.i .hg/journal.bookmarks .hg/journal.branch .hg/journal.desc .hg/journal.dirstate .hg/requires .hg/store .hg/store/00changelog.i .hg/store/00changelog.i.a .hg/store/journal.phaseroots