Windows Vista build 5212 (vbl ux dev checkin)

Windows Vista build 5212 (vbl_ux_dev_checkin) is an unleaked pre-Beta 2 build of Windows Vista.

This build notably features a new Start button that has been changed to an orb, similarly to how the "Start" text was absent in x86 pre-reset Longhorn builds with the Slate theme if the sidebar was enabled. This orb would not make it into winmain until 5252 however.