[ZD-17490]

I noticed during diagnosing a user problem that using HTTP BASIC authentication
breaks JQL search. I get errors like this:

  AxisFault
   faultCode: {http://schemas.xmlsoap.org/soap/envelope/}Server.userException
   faultSubcode:
   faultString: com.atlassian.jira.rpc.exception.RemoteValidationException: Query validation failed: The value 'ABC' does not exist for the field 'project'. Field 'fixVersion' does not exist or this field cannot be viewed by anonymous users.
   faultActor:
   faultNode:
   faultDetail:
  	{}com.atlassian.jira.rpc.exception.RemoteException:null
  	{http://xml.apache.org/axis/}hostname:kohsuke.atlassian.net

When I manually call getIssuesFromJqlSearch with other searches, no query returns
any results whatsoever.

It turns out that if I disable useHTTPAuth, it starts working again.

I couldn't find out why this "HTTP basic auth" feature was added, so I'm adding
a cautionary note to warn users. If someone understands the point of the HTTP basic
auth option, please update the documentation accordingly.