Fix deprecation warnings emanating from HttpComponents HttpClient

    [javac] C:\wip\mcf\trunk\connectors\wiki\connector\src\main\java\org\apache\manifoldcf\crawler\connectors\wiki\WikiConnector.java:1992: warning: [deprecation] UTF_8 in HTTP has been deprecated
    [javac]     method.setEntity(new UrlEncodedFormEntity(pairs, HTTP.UTF_8));
    [javac]                                                          ^
    [javac] C:\wip\mcf\trunk\connectors\wiki\connector\src\main\java\org\apache\manifoldcf\crawler\connectors\wiki\WikiConnector.java:4648: warning: [deprecation] getContentCharSet(HttpEntity) in EntityUtils has been deprecated
    [javac]         String charSet = EntityUtils.getContentCharSet(entity);
    [javac]                                     ^