Updated xhgui and removed conflicts with xhprof

I wanted to update the formula of xhgui to the latest version available on github and I've noticed that xhprof has been defined a conflictual package. I have contacted the author of xhgui which has confirmed that the `preinheimer/xhprof` build used in the existing formula is a totally separate project from xhgui.

The new xhgui version works perfectly with the original `facebook/xhprof` repository, which means that we can continue to rely on the `php5*-xhprof` module that homebrew-php already offers.