Mention proxy and https in the password prompts, with tests.
* bzrlib/transport/http/_urllib2_wrappers.py: (AbstractAuthHandler.get_password): Use our specific prompt building to address proxy and https needs. (AbstractAuthHandler._build_password_prompt): New method, helper to build the prompt. (HTTPAuthHandler.build_password_prompt): Default implementation is ok. (ProxyAuthHandler.build_password_prompt): Prefix with 'Proxy '.
* bzrlib/tests/test_http.py: (TestAuth.test_prompt_for_password): Check the prompt too.
* bzrlib/tests/test_config.py: (TestAuthenticationConfig.test_default_prompts): Delete HTTP tests which need special handling.
* bzrlib/transport/http/_urllib2_wrappers.py: (AbstractAuthHandler.build_password_prompt): New method to build the prompt and mention the protocol sed (http or https). (ProxyAuthHandler.build_password_prompt): Put proxy in front of the prompt.
* bzrlib/config.py: (AuthenticationConfig.get_password): Simplified by taking out http specifics (which were not enough to address all the cases anyway).