typecheck code

[julie Sullivan]

>If dummy and dummy2 are of different types, then when you try and do a
>pointer comparison (&dummy == &dummy2) it will produce a compiler
>warning/error.

O--ooohhh...
I came across this ages ago when I was trying to unravel the jiffies
wraparound macros and I've been scratching my head ever since trying
to figure out what this line _really_  did. A bit arcane, isn't it?
Thanks a lot Dave and everyone for explaining.

Cheers
Julie