Fixed typo instanceof/isinstance

darcs-hash:20081230102906-1e3d8-eeafc2ff59331e328c2aeb8f164935bff44dbe0a
Fixed handling of place-is in sip_subscribe_presence

darcs-hash:20081230102934-1e3d8-0d84ff9c0f57587d8178987331793ab4c2cad35e