Adapted sip_subscribe_xcap_diff to new basic SIP objects

Ignore-this: e9870fdec720cd83570fa29d664cdf37

darcs-hash:20090616101631-1e3d8-c0740cd615d0516235780dc253943e6bbcdfb246
Modified SIPURI to allow port 0

Ignore-this: 2aea7d8d26aac1a329e608528122c4f3

darcs-hash:20090616110532-1e3d8-5fe51338e436a163621aedcef7a2711ad7ba6f0b