Use TEquals() instead of T() to assert equality

The output on failure is much more informative because it shows you the
actual unexpected value.
Add "Accept:*/*" header when GETting attachments

Otherwise couch.js adds an "Accept:application/json" header, which will
cause a conforming HTTP server to return a 406 when the attachment is of
a different MIME type. (CouchDB is not conforming, so this issue didn't
show up till I tried running against Couchbase Lite.)
Fixes for attachment_names test

* Shouldn't test for hardcoded Etag values; they're implementation-
  dependent.
* Test for leading underscores wasn't working correctly (Test failure in
  try block gets caught by the catch and misinterpreted.)
'server.uri' file generated by test harness should be ignored by Git
Improvements for testing against non-CouchDB implementations

* attachments.js should set "Accept: */*" when getting text data.
* attachments.js shouldn't rely on test files in Futon (/_utils).
* Made the errors thrown by couch.js more informative.
* Fixed some syntax errors in map functions in view_update_seq.js;
  JavaScriptCore complains about the misplaced semicolons.