Remove endpoints of unbound exporters

Also, use a lock to protect against concurrent bind/unbind exporter and
service events
Merge branch 'dev' of github.com:tcalmant/ipopo into dev
iPOPO event listeners are called outside the listeners lock

The list of listeners to call is prepared inside the lock
StoredInstance private methods doesn't need to lock

... they are already called inside a lock context
JSON-RPC: Corrected "update_export"

When only properties were updated, the update was refused has the name
was already taken by the updated endpoint itself

Also, exceptions messages have been corrected (missing format)
Threads of the HTTP Service now have a name

Simplifies debugging