Hey, wouldn't it be nice to be able to add my own menu items in the Web Client?  Yes it would and now you can, if you are willing to dirty your hands with a little JavaScript.

The code

This is the add-on that I included in the CustomScripts folder

//It's a good idea to wrap your code in a function to avoid conflict
//overriding existing variables and other addon
var RMVersionListAddon = function () {
    var buttonCaption = "Show all versions";
    var versionListButton = new HP.HPTRIM.Addon.RecordAddonButton({
        caption: buttonCaption,
        clickHandler: function () {
            var cntx = this.context;
            $.getJSON(HPRMWebConfig.virtualDirectory + "HPRMServiceAPI/Record?pageSize=2&q=allVersions:" + cntx.Uri, function (data) {
                if (data.Results && data.Results.length > 1) {
                    // window.location.href = '?t=Record&q=allVersions:' + cntx.Uri;
                    $('#global-search-input').val('allVersions:' + cntx.Uri);

                    var trimApp = window['root'];
                    trimApp.trimGlobalSearchPanel.search('allVersions:' + cntx.Uri);
                } else {
                    alert("There are no versions for this Record.")
                }
            });           
        }
    });

    //Prerender should have the context object
    versionListButton.preRender = function () {
        var record = this.context;
        if (record.RecordRecordType.RecordTypeAllowVersions.Value !== true) {
            this.setVisible(false);
        }
    };

    HP.HPTRIM.Addon.CustomScriptManager.register(versionListButton);

}();

Debugging

Don't forget you can swith debugging on to get a better view of your code, like this:

<compilation debug="true" targetFramework="4.5" />