This patch creates an "About Blender" popup dialog.
I find it very odd that we have a pulldown menu attached to the "blender" logo. I'm certain that we have many users who are unaware that there is a menu there at all, and have never seen the options on it. This proposal is mostly a means to (eventually) remove that menu.
Instead this adds a new item to the File Menu:
It brings up version details, links, and more information in a form that many users will consider standard and normal. Clicking outside the dialog, or hitting "esc", or clicking the button will close it.
Because this is a nice place to put complex version details, like hash etc, this means we can simplify the Splash screen so that it only contains the version string. That makes the version more prominent without the competing content, and also treats the splash image a little nicer by having less occluding text.