fix setting a property to a falsy value with message send
Merge branch 'master' into pr-1014
extending tests to other failing falsy cases
Fixing falsy value assigns in JSObjectProxy
Eschewing .slice()ing the arguments.

Only way the object is used in passing it along, reading .length and [0].
Therefore there is no need to actually copy it, it can be passed as-is.
Merge pull request #1015 from herby/fixing-calljs-falsy

Fixing calljs falsy