Remove references to using basic auth in userstream (Twitter removed basic auth option on 2013-06-11)
Added user and site stream support to the Phirehose base class. (I.e. added two constants, made URL_BASE a member variable instead of a const, and made setFollow() be usable for METHOD_SITE too).

The UserstreamPhirehose class was then derived from OauthPhirehose, meaning it could be stripped back to almost no functionality. (Also added an example script (userstream-alternative.php) to show that in fact you can do user streams by using OauthPhirehose directly.)

Minor: added $lang parameter to UserstreamPhirehose constructor.

Note: you now only need to include one header (either lib/OauthPhirehose.php or lib/UserstreamPhirehose.php), as the other library files include their dependencies now.

NOTE: the Site stream functionality is basic (only the follow parameter supported), and untested. example/sitestream.php

Userstream testing was confirmed to work for: my tweet, adding a new friend, someone retweeting me, me retweeting someone, deleting my test tweets.