Use UA string as User-Agent header for XCAP requests

Ignore-this: dbe40939cc053091768b24e35a89ede4

darcs-hash:20101011080457-56b4d-c4eacd2dee6982c817f463c3a5d4a9b4e9035234
Fixed incorrect __hash__ method

Ignore-this: 65516f49e9df77a7a1e7027c5bb9feb2

darcs-hash:20101012121408-b22ec-619152335339e0adb9785865df99a1904536afcc