hgweb: do not try to replace signal handlers while locking
According to the issue 5889, mod_wsgi issues a warning on signal.signal()
call, and we wouldn't want to see it in error log. The problem addressed
by
d77c3b023393 could potentially occur in web session, but that would be
less likely than in user processes.
Test issue2761
$ hg init
$ touch to-be-deleted
$ hg add
adding to-be-deleted
$ hg ci -m first
$ echo a > to-be-deleted
$ hg ci -m second
$ rm to-be-deleted
$ hg diff -r 0
Same issue, different code path
$ hg up -C
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ touch does-not-exist-in-1
$ hg add
adding does-not-exist-in-1
$ hg ci -m third
$ rm does-not-exist-in-1
$ hg diff -r 1