Quicker way of handling empty for loops.

Oftentimes you need to do something special if a for loop will not ever run; that is, the loop condition is false even before we ever iterate into the for loop. We propose a new keyword, 'empty', which can be added onto a for loop. This code will be called if the for loop's loop condition is false right away.

old code:

     int length = someObject.size();
     if ( length == 0 ) {
          throw new EmptyCollectionException();
     }
     for ( int i = 0 ; i < length ; i++ ) {
          // ... whatever
     }

new code:

     for ( int i = 0 ; i < someObject.size() ; i++ ) {
          // ... whatever
     } empty {
          throw new EmptyCollectionException();
     }

BONUS: Add a pythonesque 'else' statement as well, which is called when the for loop exits normally (but not if the for loop ends abruptly, by an in-for return or throws statement, a break statement, or a continue jumping to an outer label. I don't think 'else' is the proper term for it, though.

BACKWARD COMPATIBILITY PROBLEMS: 'empty' is not currently a reserved keyword. An existing reserved keyword, such as 'else' can be used for this, but 'else' is a really bad idea. Python supports 'else' on a for loop but its meaning is completely different.