xml export plugin - bug correction

[kermorgant]

There is a bug in the XML export plugin, which occurs when :

* there are 2 or more events in a reservation
* some resources are not booked for all these events (ie exclusions are done)

The current version does not take into account these exclusions, so here is a new version that corrects that.

Regards,

Mikael Kermorgant

[kermorgant]

Main code for the XML export Plugin