loop over range should use 'int' variable if endpoints are 'small'

Given:

for (i in 0:10) { ... }
for (i in 1..10) { ... }

Or:

small Integer x = 0;
small Integer y = 10;
for (i in x:y) { ... }
for (i in x..y) { ... }

The compiler should use an int for the loop variable i.

[gavinking]

That would be fine by me.

[tombentley]

@xkr47 FTR JVM microbenchmarks have shown that a java for loop over an int is much faster than the same loop using a long. So this would be a worthwhile optimization to have.