Fix test-desugar command.

The `-print` option no longer seems to be valid.
Make the "source" field optional.

This allows LambdaS5 to consume the ASTs produced by Esprima, which lack the
"source" property.
Throw an error if a for-each loop is encountered.
Fix spelling and whitespace.
Merge pull request #29 from int3/master

Miscellaneous fixes.