Remove Authenticator class code from URLHelper

The createFileFromUrl and resolveUrl methods in URLHelper currently use an Authenticator implementation for providing username/password credentials when accessing URLs, notably HTTP. However, due to a JVM bug [1] the credentials are cached for the duration of the JVM session and cannot be reset. Thus, once the Authenticator class has been set, it cannot be changed. The effect of this is that the user can enter the wrong credentials for a WSDL once in a wizard and can never change them.

Replace the Authenticator implementations in URLHelper with a method to set an http request property instead, eg.

urlConn.setRequestProperty("Authorization", "Basic " + Base64.encodeBytes((userName + ':' + password).getBytes()))

[1] http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6626700