Global scope pollution checks included in test suite

This is an output example of running the tests with some missing local statements:

```
~/git/luafun/tests$ ./runtest *.lua
Testing basic.lua
Testing compositions.lua
Testing filtering.lua
Testing generators.lua
Testing indexing.lua
Testing operators.lua
Testing reducing.lua
Testing slicing.lua
Testing transformations.lua

Some global variables have been declared by mistake:
634 : function all() = var 'r'
783 : function tomap() = var 'val'
783 : function tomap() = var 'key'
769 : function totable() = var 'val'

Please declare them with the local statement
```