Customizable prefix of the help block id

[Branko Vukelic]

The id attribute of the help block should be customizable. The API should be simple. We pass an options object to the $.fn.autohideHelp call in the following format:

$(selector).autohideHelp({
    blockId: value
});

The value can be either a string or a function. If it is a function, we will treat it as a prefix. If it is a function, it will be passed the id of the form field, and it would be expected to return a string that we can use as a jQuery selector.