Bring back foreach int indexes

[Steven Schveighoffer]

I don’t know how many times I get caught with size_t indexes but 
I want them to be int or uint. It’s especially painful in my 
class that I’m teaching where I don’t want to yet explain why int 
doesn’t work there and have to introduce casting or use to!int. 
All for the possibility that I have an array larger than 2 
billion elements.

I am forgetting why we removed this in the first place.

Can we have the compiler insert an assert at the loop start that 
the bounds are in range when you use a smaller int type? Clearly 
the common case is that the array is small enough for int indexes.

-Steve