The way these definitions worked before, they did not handle quoted args
with spaces properly.
For example, if you had `/tmp/test-just/printlen.py` as:
```python
#!/usr/bin/env python3
import sys
print(len(sys.argv))
```
and your `justfile` was:
```
printlen *args:
/tmp/test-just/printlen.py {{args}}
```
Then:
```shell
$ just printlen foo bar
3
$ just printlen 'foo bar'
3
```
which is not what we want: `'foo bar'` should be treated as one
argument.
The fix is to use
[positional-arguments](515e806b51/README.md (L1131)):
```
set positional-arguments
printlen *args:
/tmp/test-just/printlen.py "$@"
```
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