[server] add a looping task to free unused cnxsets capture by dead pyro
When a pyro client disconnects, we're not necessarily notified so they
can hang on to their session/cnxset forever. Don't let them do that.
The hacky looping task is only installed when pyro is enabled. This optional
activation save this very hacky patch from being rejected.
closes #2825380
[devtools] Use XMLValidator instead deprecated SaxOnlyValidator
The renaming was introduced in 198fdadafed6.o
This prevent a meta class conflict introduced by logilab-common 0fcd2e050621.