Etags should be quoted

HTTP 1.1 specifies that Etag values are delimited by double-quotes; this affects headers Etag, If-Match, If-None-Match, etc. Sync Gateway isn't doing this in some cases.

• The admin API for accessing the config (admin_api.go) both sets and reads unquoted etags.
• doc_api.go appears to set quoted Etag: headers, but when it reads If-Match: headers it doesn't unquote them. As far as I can tell, this breaks conditional GETs of documents. I don't think that feature is being tested properly
• api_test.go isn't detecting the above bug – it expects the quotes when it looks at document Etags, but when it generates If-Match headers for requests it doesn't quote them. In other words it isn't acting like a real client and sending back the same Etag it received.