/brz/remove-bazaar

Review feedback.

* doc/en/user-guide/authentication_conf.txt: 
New file. Authentication configuration file documentation.

* doc/en/user-guide/configuration.txt: 
Slight modifications, add authentication.conf reference.

* doc/en/mini-tutorial/index.txt: 
Fix make docs warning.

* doc/developers/authentication-ring.txt: 
Small cleanups noticed during
doc/en/user-guide/authentication_conf.txt redaction.

* bzrlib/transport/http/_urllib.py:
(HttpTransport_urllib._perform): Use a dict() instead of {} syntax.

* bzrlib/tests/blackbox/test_whoami.py:
(TestWhoami.test_whoami_branch): Delete BZREMAIL related tests.

* bzrlib/config.py:
(Config.username): BZREMAIL deleted, has been obsolete for more
than a year.
(AuthenticationConfig.__init__): Review feedback, since keeping a
callback as an attribute is useless, call it now and keep the
filename itself as an attribute.
(AuthenticationConfig.get_credentials): Use a dict() instead of {}
syntax.

* NEWS: 
Updated as per Martin's suggestion.