Implementing issue #200, change the test for username capitalization
variation during login from insensitivity to sensitivity.
(Whoops, we don't actually need to add app initialization to the changed
test.)
Implementing issue #200, refuse a successful login if the actual username
varies from the one the user provided.  (The server allows username case
variation.)

Inhibit caching in the ajax login and logout calls, or case variations will
eventually be mishandled.
Merge pull request #201 from SpiderOak/issue-200-case-sensitive-username

Issue 200 case sensitive username