Added payload parsing to sip_subscribe_xcap_diff

Ignore-this: 5e2269ed9ecb62eb45d7b9038c02537e

darcs-hash:20090520064248-1e3d8-4fb3b0b62eba1230777cf15a7b080edde403c060
Fixed path_regex of sipsimple.applications.util.XCAPURI

Ignore-this: d6c6bef5f3e3f5ec9e985ebe8dbd69e6

darcs-hash:20090520064537-1e3d8-e322ba783e972c0f2e07c954e6deccb4689019e2