plugins (jingle) file transfer: use initial "from" attribute as local jid instead of client.jid: while client.jid is fine in a client context, for components it's not the right jid to use: it is the jid of the component itself while the file transfer/jingle session entity may be established with this jid + a local part (e.g. if client is files.example.net, session may be established with louise@files.example.net, in which case "from" is louise@files.example.net, while client.jid will be files.example.net). As a consequence, using client.jid was causing trouble with components. This patch fixes it for jingle and plugins linked to file transfer by keeping a "local_jid" variable in the session, where the jid from the original "from" attribute is used.