I noticed that some files in rubygems were executable, and I could think
of no reason why they should be.

In general, I think ruby files should never have the executable bit set
unless they include a shebang, so I run the following command over the
whole repo:

```bash
find . -name '*.rb' -type f -executable -exec bash -c 'grep -L "^#!" $1 || chmod -x $1' _ {} \;
```

Currently, there is not a way to create a sized enumerator in C
with a different set of arguments than provided by Ruby, and
correctly handle keyword arguments.  This function allows that.

The need for this is fairly uncommon, but it occurs at least in
Enumerator.produce, which takes arugments from Ruby but calls
rb_enumeratorize_with_size with a different set of arguments.