Setting array length without initializing/reallocating.

[Jonathan Levi]

Wow, there went several hours of debugging.

Increasing the length of a slice, by setting its length, will 
initialize the new elements and reallocate if necessary.

I did not realize length was "smart", I guess I should have 
guessed.

Anyway, to work around this, and probably also be more clear, 
create a new slice from the same pointer.

`array = array.ptr[0..newLength];`