manifestcache: protect write with `wlock` instead of `lock`
The `wlock` is taken by both `update` and `commit` type operation. This would
help persisting the cache more aggressively.
An explicit test is introduced. However, we can already see the effect of this
change on earlier test output.
$ hg init test
$ cd test
$ hg debugbuilddag '+2'
$ hg phase --public 0
$ hg serve -p $HGPORT -d --pid-file=hg.pid -E errors.log
$ cat hg.pid >> $DAEMON_PIDS
$ cd ..
$ hg init test2
$ cd test2
$ hg incoming http://foo:xyzzy@localhost:$HGPORT/
comparing with http://foo:***@localhost:$HGPORT/
changeset: 0:1ea73414a91b
user: debugbuilddag
date: Thu Jan 01 00:00:00 1970 +0000
summary: r0
changeset: 1:66f7d451a68b
tag: tip
user: debugbuilddag
date: Thu Jan 01 00:00:01 1970 +0000
summary: r1
$ killdaemons.py
$ cd ../test
$ hg --config server.view=immutable serve -p $HGPORT -d --pid-file=hg.pid -E errors.log
$ cat hg.pid >> $DAEMON_PIDS
$ cd ../test2
$ hg incoming http://foo:xyzzy@localhost:$HGPORT/
comparing with http://foo:***@localhost:$HGPORT/
changeset: 0:1ea73414a91b
tag: tip
user: debugbuilddag
date: Thu Jan 01 00:00:00 1970 +0000
summary: r0
$ killdaemons.py